WO2010122321A2

WO2010122321A2 - Conception calculators

Info

Publication number: WO2010122321A2
Application number: PCT/GB2010/050437
Authority: WO
Inventors: Christopher Bruce Everett; Kenneth Stanley Targett
Original assignee: Christopher Bruce Everett; Kenneth Stanley Targett
Priority date: 2009-04-23
Filing date: 2010-03-12
Publication date: 2010-10-28
Also published as: GB2459378A; GB2459378B; WO2010122321A3; GB0906905D0; GB2459378A8

Abstract

A conception calculator (410) comprises a calendar slide (414) and an indicator slide (412) that are relatively rotatable. The calendar slide is divided into at least three, but preferably less than twelve, month-segments (424A-C). The indicator slide is marked with, or is set out to be marked with, a fixed start-of-last-period indicator (462), which a user can align with that one of the divisions of a scale on the calendar slide corresponding to the date of the start of her last period. The indicator slide is set out to be marked with a fixed fertility indicator (464) which is angularly offset from the start-of-last-period indicator and which indicates on the calendar scale a sequence of days-of-the-month when the user can expect to be fertile. The angular offset of the indicators and the number of days in the sequence indicated by the fertility indicator are both preferably arranged to be determined in dependence upon the values of two numeric parameters related to the user's menstrual cycle history (for example her shortest cycle length and her variation in her cycle lengths in recent months) so as to personalise the calculator. The calculator therefore takes account of the user's menstrual history yet employs only two slides, as a result of which the calculator is of simple and inexpensive construction and, once personalised, is easy to use, requiring only one movement of the two relatively-movable slides in order to set the start date of the last period.

Description

Description Conception calculators

[1] This invention relates to conception calculators, particularly those of the circular slide rule type.

[2] It is useful for a woman to know when sexual intercourse may result in conception, either so as to avoid pregnancy or alternatively so that intercourse can be timed so as to coincide with the time in her monthly menstrual cycle when she will possibly or probably be fertile, so as to increase the probability of intercourse resulting in pregnancy. It is also useful for a woman to know when her next menstrual period will begin, so that any necessary steps can be taken. A typical sperm has a lifespan of approximately five days after intercourse. A typical unfertilised egg has a lifespan of approximately one day after ovulation. As a result, there is a window of approximately six or seven days within which intercourse is most likely to result in conception. For most women, their next period begins approximately fourteen days after ovulation, provided that an egg has not been fertilised. However, for many women, their cycle length is not constant, but varies from month to month. (In this specification, "cycle length" means the number of days from the start of one menstrual period, i.e. the start of bleeding, until the start of the next.) Therefore, for those women, ovulation does not occur a constant number of days after the start of their last period, and it is therefore not possible to predict in advance the precise day of ovulation. However, by knowing both their shortest cycle length and their longest cycle length in recent months, it is possible to predict a range of dates when ovulation can be expected to occur. From that, it is possible to predict a range of dates when intercourse is likely to result in fertilisation of the egg. It is also possible to predict a range of dates when their next period can be expected to start, assuming that they have not fallen pregnant. A number of circular slide-rule calculators have been proposed in the past to assist in calculating the date(s) when intercourse is most likely to result in fertilisation and/or the date(s) when the next period can be expected to start. However, problems associated with such calculators are that: the months of the year do not have the same number of days; February has a different number of days depending on whether or not it is a leap year; different woman have monthly cycles of different average lengths; and the length of a particular woman's cycle can vary from one month to another. It is also desirable that any such calculator be accurate, easy to use, relatively small, rugged and inexpensive to produce. The backround art to the present invention includes patent documents US4737619, GB 1252611, US3771716, SU1772800A1, GB759192, US2076242 and US2792177. A detailed discussion of this prior art is given in patent document GB2459378A. [3] An aim of a first aspect of the present invention, or at least of specific embodiments of it, is to provide a conception calculator of the circular slide -rule type that: (a) requires only two slides in order to produce conception calculations for the whole year, so that the calculator can be of simple construction and requires only one rotational setting as between the two slides for each calculation; (b) takes account of the different numbers of days in the calendar- months; (c) takes account of different users' different cycle lengths; and (b) takes account of variations in a particular user's cycle lengths. In accordance with the first aspect of the present invention, there is provided a conception calculator as defined in claim 1. The first aspect of the invention recognises that parameters such as a particular woman's shortest and longest cycle lengths in recent months remain constant over a prolonged length of time. It is therefore unnecessary to provide a respective pair of relatively-movable slides in order to set each of the historic parameters into the calculator. Instead, the calculator of the first aspect of the invention is arranged to be calibrated or personalised with such parameters by marking the indicator scale with fixed indicators. The calculator therefore takes account of the user's menstrual history yet employs only two slides, as a result of which the calculator is of simple and inexpensive construction and, once personalised, is easy to use, requiring only one movement of the two relatively-movable slides in order to set the start date of the last period. In a first embodiment, the indicator slide is as defined in claim 2. In this case, the indicator slide is preferably as defined in claim 3, and more preferably as defined in claim 4. As will be appreciated from the following detailed description, the different manners in which the fertility indicator is marked (for example forward- slashes, back-slashes and both, i.e. crosses) can be used to indicate different probabilities of fertility for different days. In second and third embodiments, the indicator slide is as defined in claim 5. In particular, in the second embodiment, the indicator slide is as defined in claim 6, and more preferably as defined in claim 7. Again, the different manners in which fertility indicator is marked (for example forward- slashes, back-slashes and both, i.e. crosses) can be used to indicate different probabilities of fertility for different days. By contrast, in the third embodiment, the indicator slide is as defined in claim 8, and more preferably as defined in claim 9. The indicator slide may be as defined in claim 10, 11, 12 or 13. The calculator may be as defined in claim 14. Each of the numeric parameters referred to can be determined easily and accurately. The accuracy of the calculator is then reliant on the assumption that, for all women, ovulation occurs a predetermined number of days (for example fourteen days) before the start of the next period. The calcualtor is more preferably as defined in claim 15. This is particularly advantageous in the case of the first embodiment so as to reduce or obviate any overlap of the start-of-last-period and fertility scales. It is possible for a woman to determine when she ovulates, for example by monitoring her basal body temperature, her cervical position and texture and/or her cervical mucus, or by using an ovulation kit to test her urine and/or saliva. She can then determine her shortest and longest ovulation intervals and her variation in ovulation intervals. (In this specification, "ovulation interval" means the number of days from the start of a menstrual period until the day of ovulation.) In this case, the calculator may be as defined in claim 16. Ovulation interval is more difficult to determine than cycle length, and there may be inaccuracies in the determined intervals, but the calculator does not then need to rely on any assumption regarding the length of time between ovulation and the start of the next period. The calcualtor is more preferably as defined in claim 17. Again, this is particularly advantageous in the case of the first embodiment so as to reduce or obviate any overlap of the start- of- last-period and fertility scales. Preferably, the calculator is as defined in claim 18, rather than having twelve month-segments, so that each day-division can occupy more than l/365th of the calendar scale (about 1.0°). This latter feature may be provided independently of other features of the first aspect of the invention. Therefore, in accordance with a second aspect of the present invention, there is provided a conception calculator as defined in claim 19. One version of the calendar scale is defined in claim 20, so that there are two hundred and eleven such day-divisions in total (about 1.7° each). For the same diameter of calendar scale, this substantially increases the size of each day-division compared with a scale having three hundred and sixty-five day divisions, and yet the layout does not cause any date calculation errors, even in a leap year, unless the user's longest cycle length is greater than about seventy-five days (which is an extraordinarily long cycle length), or unless the user's longest cycle length is greater than about sixty days (which is also an extraordinarily long cycle length) if the start-of-next-period calculating function is being employed. Another version of the calendar scale is defined in claim 21, so that there are one hundred and fifty-one such day-divisions in total (about 2.4° each). For the same diameter of calendar scale, this substantially increases the size of each day-division even more, but it can cause a date calculation error or problem in a leap year if 29th February falls within the interval being calculated. The calculation may be one day out, or it may not be possible to set the slides properly if the user's last period started on 29th February. A further version of the calendar scale is defined in claim 22, so that there are one hundred and eighteen such day-divisions in total (about 3.1° each). For the same diameter of calendar scale, this substantially increases the size of each day-division even more, and yet the layout does not cause any date calculation errors as a result of a leap year. However, date calculation errors can arise if the user's longest cycle length is greater than about forty- five days (which is an unusually long cycle length), or if the user's longest cycle length is greater than about thirty days and the start-of-next-period calculating function is being employed. Yet another preferred version of the calendar scale is defined in claim 23, so that there are only eight-nine such day-divisions in total (about 4.0° each). For the same diameter of calendar scale, this substantially increases the size of each day- division even more, but can cause the date calculation error or problem in a leap year. Nevertheless, provided that the user's longest cycle length is no longer than about forty-five days (which applies to the vast majority of women), this layout can result in a calculator which is easy to set and read and which provides an accurate calculation of the most fertile phase, except possibly once every four years. With these relatively large day-divisions, compared with a calendar scale having 365 day-divisions, the calcualtor is preferably as defined in claim 24.

[4] Specific embodiments of the present invention will now be described, purely by way of example, with reference to the accompanying drawings. Figures 1 to 4 relate to one embodiment of conception calculator, and in particular: Figures 1 and 2 are plan views of its indicator slide and a calendar slide, respectively; Figure 3 is a plan view of the calculator, calibrated for a shortest cycle length of thirty days and variation of four days, and set for a last-period- start-date of 10th February; and Figure 4 is a cross- sectioned side view of the calculator. Figures 5 to 8 relate to another embodiment of conception calculator, and in particular: Figures 5 and 6 are plan views of its indicator slide and a calendar slide, respectively; Figure 7 is a plan view of its indicator slide, after calibration for a shortest cycle length of thirty-two days and a variation of one day; and Figure 8 is a plan view of the assembled calibrated calculator, set for a last- period-start-date of 14th June. Figures 9 to 12 relate to further embodiment of conception calculator, and in particular: Figures 9 and 10 are plan views of its indicator slide and a calendar slide, respectively; Figure 11 is a plan view of its indicator slide, after calibration for a shortest cycle length of twenty-four days and a longest cycle length of twenty-seven days; and Figure 12 is a plan view of the assembled calibrated calculator, set for a last-period-start-date of 29th January. Figures 13 to 17 relate to further embodiment of conception calculator, and in particular: Figures 13 and 14 are plan views of its indicator slide and a calendar slide, respectively; Figure 15 is a plan view of a sheet of calibration stickers; Figure 16 is a plan view of the indicator slide, after calibration for a shortest cycle length of twenty-six days and a variation of three days; and Figure 17 is a plan view of the assembled calibrated calculator, set for a last- period-start-date of 17th February. Figures 18 to 20 are plan views of other versions of the calendar slide.

[5] Referring to Figures 1 to 4, a conception calculator 110 comprises a generally rectangular indicator slide 112 and a circular calendar slide 114, each printed and each made of card, plastics laminated card, or sheet plastics material. The slides 112,114 are joined for relative rotation by a rivet 116 through a hole 118 at the centre of the circular calendar slide 114 and a hole 120 at the centre, or somewhere near the centre, of the rectangular indicator slide 112. In a typical example, the calendar slide 114 has a diameter D of 120 mm, and indicator slide 112 has a width W of about 190 mm and a height H of about 150 mm. The periphery of the calendar slide 114 is printed with a calendar scale having eighty-nine day-divisions 122 at an angular pitch P of 360/89°. The calendar slide 112 is also divided into three month- segments 124A,124B,124C by dividing lines 126. One of the month- segments 124 A contains thirty-one of the day- divisions 122 numbered "1" to "31" clockwise around the slide 112 and is printed with a label 128 A indicating that it is for a thirty-one day month, for example with the text "Set disc using this segment if last period started in a 31-day month (January, March, May, July August, October or December)." The next month-segment 124B in the clockwise direction contains thirty of the day-divisions 122 numbered "1" to "30" clockwise around the slide 112 and is printed with a label 128B indicating that it is for a thirty day month. The remaining month-segment 124C contains twenty-eight of the day-divisions 122 numbered "1" to "28" clockwise around the slide 112 and is printed with a label 128C indicating that it is for February or a twenty-eight day month. With the calendar slide 114 having a diameter D of 120 mm, each of the eighty-nine day- divisions 122 can be individually numbered with a digit height of 2.5 mm without the digits overlapping each other or the fine dividing-lines between the day-divisions 122, and the calendar scale is therefore easily readable. The indicator slide 112 is printed with an arcuate start-of- last-period scale 130 centred on the hole 120 and having a series of fifteen "squares" 132 lying outside the diameter D of the calendar slide 114 at the angular pitch P of 360/89° with numbering 134 from "35" to "21" in the clockwise direction. The start-of-last-period scale 130 has a label 136 reading, for example, "Set start of last period", and is also marked with a calibration instruction 138 reading, for example, "Calibration: Mark "X" in the square for your shortest cycle length." The indicator slide 112 is also printed with a fertility scale 140 centred on the hole 120 and having a series of sixteen "squares" 142 lying outside the diameter D of the calendar slide 114 at the angular pitch P of 360/89°. The squares 142 of the fertility scale 140 are numbered with a first sequence of numbering 144 from "0" to "10" in the clockwise direction starting from the most anticlockwise of the squares 142, and with a second sequence of numbering 146 from "0" to "10" in the clockwise direction starting from the square 142 that is numbered "6" in the first sequence of numbering 144. The squares 142 that are numbered "0" to "6" in the first sequence of numbering 144 are each marked with a forward-slash. The fertility scale 140 has a label 148 reading, for example, "Fertility zone", and is also marked with a calibration instruction 150 reading, for example, "Calibration: Mark "\" in the two squares for your variation and in the squares in between." The indicator slide 112 is furthermore printed with an arcuate start-of- next-period scale 152 centred on the hole 120 having a series of ten "squares" 154 lying outside the diameter D of the calendar slide 114 at the angular pitch P of 360/89° with numbering 156 from "0" to "10" in the clockwise direction. The start-of-next-period scale 152 has a label 158 reading, for example, "Next period zone", and is also marked with a calibration instruction 160 reading, for example, "Calibration: Mark "X" in square "0", in the square for your variation and in the squares in between." The square 154 numbered "0" in the start-of-next-period scale 152 is angularly offset clockwise from any square 132 in the start-of-last-period scale 130 by an angle N equal to the number of that latter square multiplied by the angular pitch P. For example, the square 154 numbered "0" in the start-of-next-period scale 152 is angularly offset clockwise from the square 132 numbered "28" in the start- of-last-period scale 130 by an angle N = (28x360)/89°. The square 142 numbered "5" in the fertility scale 140 is angularly offset anticlockwise from the square 154 numbered "0" in the start-of-next-period scale 152 by an angle O equal to fourteen times the angular pitch P, i.e. O = (14x360)/89°. The conception calculator 110 may be provided with an instruction leaflet (not shown) and/or may also be printed with further instructions on the front of the slides 112,114 or on the rear of the indicator slide 112. The instructions tell the user that, in order to calibrate her calculator 110, she needs to determine her shortest and longest historical cycle lengths in recent months, for example in the last six to twelve months. She then needs to calculate her historical variation in cycle lengths, which is equal to her longest historical cycle length minus her shortest historical cycle length. The leaflet, or a space on the calculator 110, may be set out as a table in which the user can keep a log of the dates on which her periods start and a list of her cycle lengths to assist in working out her shortest and longest cycle lengths and the variation in them. The instructions tell her that she then needs to mark a cross in the square 132 of the start-of-last-period scale 130 numbered with her shortest cycle length. Also, on the fertility scale 140, she needs to mark a back-slash in the square 142 numbered in the first, left-hand sequence 144 with her variation, a backslash in the square 142 numbered in the second, right-hand sequence 146 with her variation, and in each square 142 between those two squares. Furthermore, on the start- of-next-period scale 152, she needs to mark a cross in the square 154 numbered "0", a cross in the square 154 numbered with her variation (if her variation is greater than zero days), and cross in each square 154 between those two squares (if her variation is greater than one day). It should be noted that that, on the fertility scale 140, if her variation is zero days, the seven squares 142 previously marked with a forward- slash will become marked with crosses. If her variation is between one and six days, at least one of the squares 142 previously marked with a forward-slash will become marked with a cross, with at least one square 142 to the left of it remaining marked with a forward- slash and at least one square 142 to the right of it becoming marked with a back-slash. If her variation is at least seven days, the seven squares 142 previously marked with a forward-slash will be followed to the right by seven squares 142 marked with a back-slash. In this case, if her variation is more than seven days, there will be at least one unmarked square 142 between the seven squares 142 marked with a forward- slash and the seven squares 142 marked with a back-slash, which the user may be instructed to mark with a hyphen. In the example shown in Figure 3, the conception calculator 110 has been calibrated for a woman having a shortest cycle length of thirty days and a longest cycle length of thirty-four days, so that her variation is four days. Accordingly, the square 132 numbered "30" has been crossed on the start-of-last period scale 130 so as to form a start-of-last-period indicator 162 fixed on the indicator slide 112. On the fertility scale 140: the squares 142 numbered "0" to "3" in the first sequence of numbering 144 remain marked with back-slashes; the squares 142 numbered "4" in the first sequence of numbering 144 to "0" in the second sequence of numbering 146 have become marked with crosses; and the squares 142 numbered from "1" to "4" in the second sequence of numbering 146 have become marked with backslashes. The forward- slashed, crossed and back-slashed squares together form a fertility indicator 164 fixed on the indicator slide 112. Also, the squares 154 numbered from "0" to "4" have been crossed on the start-of-next-period scale 152 to form a start- of- next-period indicator 166 fixed on the indicator slide 112. The instructions also tell the user that, each month, she should note the date of the start of her last period. She should then select the appropriate month-segment 124A-C for the calendar- month in which her last period started. In that segment she should select the day-division 122 numbered with the day-of-the-month on which her last period started. She should then rotate the calendar slide 114 relative to the indicator slide 112 so that the selected day- division 122 becomes aligned with the start-of-last-period indicator 162. She is then instructed to note the days of the month on the calendar slide 114 which are aligned with the fertility indicator 164, and is informed that they are the days-of-the-month when she can expect to be possibly fertile, and that she can expect to be more fertile on any days-of-the-month aligned with any crosses than on any days-of-the-month aligned with any forward- slashes and back-slashes. She is also instructed to note the days of the month on the calendar slide 114 which are aligned with the start-of-next-period indicator 166, and is advised that they are the days-of-the-month when she can expect her next period to start. In the example shown in Figure 3, the calendar slide 114 has been set relative to the indicator slide 112 for the case where the user's last period started on 10th February. Accordingly, the day-division 122 numbered "14" in the month-segment 128C for a 28-day month on the calendar slide 114 has been aligned with the start-of-next-period indicator 162 on the indicator slide 112. In this position, the fertility indicator 164 on the indicator slide 112 is aligned with day-divisions 122 numbered "21" to "28" and "1" to "3" on the calendar slide 114, and the user will understand that she can therefore expect to be possibly fertile between 21st February and 3rd March. Also, the crosses of the fertility indicator 164 are aligned with the day- divisions 122 numbered "25" to "27", and the user will understand that she can therefore expect to be more fertile between 25th and 27th February. The start- of- next-period indicator 166 on the indicator slide 112 is aligned with the day-divisions 122 numbered "12" to "16" on the calendar slide 114, and the user will therefore understand that she can expect her next period to begin between 12th March and 16th March, if she has not fallen pregnant. With reference to the example shown in Figure 3, the calculator 110 is based on the the following assumptions and conclusions: a) The assumption that the user's next period can be expected to begin no sooner than her shortest historic cycle length after the start date of the last period (e.g. if her shortest historic cycle length is thirty days, and her last period started on 10th February, her next period can be expected to start no sooner than 12th March), b) The assumption that the next period can be expected to begin no later than the user's longest historic cycle length after the start date of the last period (e.g. if her longest historic cycle length is thirty-four days, her next period can be expected to begin no later than 16th March), c) The assumption that the user can be expected to ovulate fourteen days before her next period is scheduled to start, d) The conclusion from "a" and "c" that the earliest expected ovulation date is her shortest historic cycle length less fourteen days after the start date of her last period (e.g. 26th February), e) The conclusion from "b" and "c" that the latest expected ovulation date is her longest historic cycle length less fourteen days after the start date of her last period (e.g. 2nd March), f) The assumption that sperm lifespan is five days after intercourse, g) The assumption that egg lifespan is one day after ovulation, h) The conclusion from "d", f ' and "g" that, if the user is on a shortest cycle, pregnancy may result from intercourse as early as her shortest historic cycle length less nineteen days after the start date of her last period (e.g. intercourse on or after 21st February), i) The conclusion from "d", f" and "g" that, if the user is on a shortest cycle, pregnancy may result from intercourse as late as her shortest historic cycle length less thirteen days after the start date of her last period (e.g. intercourse on or before 27th February), j) The conclusion from "e", "f" and "g" that, if the user is on a longest cycle, pregnancy may result from intercourse as early as her longest historic cycle length less nineteen days after the start date of her last period (e.g. intercourse on or after 25th February), k) The conclusion from "e", "f" and "g" that, if the user is on a longest cycle, pregnancy may result from intercourse as late as her longest historic cycle length less thirteen days after the start date of her last period (e.g. intercourse on or before 3rd March). 1) The conclusion from "h" and "k" that pregnancy may, or may not, result from intercourse between: (1) her shortest historic cycle length less nineteen days after the start date of her last period and (2) her longest historic cycle length less thirteen days after the start date of her last period, depending on the current cycle length (e.g. intercourse between 21st February and 3rd March), m) The conclusion from "i" and "j" that, if the user's longest historic cycle length less her shortest historic cycle length (i.e. her variation) is no more than six days, pregnancy may result from intercourse between: (1) her longest historic cycle length less nineteen days after the start date of her last period and (2) her shortest historic cycle length less thirteen days after the start date of her last period, regardless of the current cycle length, provided that it is between the historic shortest and longest cycle lengths (e.g. intercourse between 25th and 27th February). It will be appreciated that there may be some debate as to the exact number of days to be used for assumptions "c", "f" and "g" above, and that the angle O and the numbering 144,146 of the calculator 110 may be modified accordingly.

[6] The embodiment of Figures 5 to 8 is identical to the embodiment of Figures 1 to 4 described above, except in the following respects. In Figures 5 to 8, features that are identical to or correspond to features in Figures 1 to 4 are referenced with reference numerals that are 100 greater than those in Figures 1 to 4. Referring to Figures 5 and 7, the numberings 234,244,248,256 of the start-of-last-period scale 230, fertility scale 240 and start-of- next-period scale 252 are disposed on the indicator slide 212 inside the outline 268 of the calendar slide 214, and the calibration instructions 238,250,260 are disposed radially inwardly of the numberings 234,244,248,256. Accordingly, the labels 236,248,258 for the start-of-last-period scale 230, fertility scale 240 and start- of- next-period scale 252 can be disposed on the indicator slide 212 closer to the scales 230,240,252, and the indicator slide 212 can be reduced in size, for example to a width W of about 165 mm and a height H of about 140 mm. The calendar slide 214 is flexible, so that it can be lifted away from the indicator slide 212 so that the user can read the instructions 238,250,260 and the numberings 234,244,248,256 of the scales 230,240,252 during calibration. Alternatively, the rivet may be replaced by a rotatable pop-stud 216 that allows the slides 212,214 to be rotated relative to each other, but also allows the calendar slide 214 to be temporarily removed from the indicator slide 212 when the indicator slide 212 needs to be calibrated and then replaced. As a result, the indicator slide 212 has a less cluttered appearance (compare Figures 3 and 8) when the calculator 210 is being used after calibration. The indicator slide 212 is shown in Figures 7 and 8 calibrated for a shortest cycle length of 32 days and a variation of 1 day. The calendar slide 214 is shown set in Figure 8 against the start-of-last-period indicator 262 for a last period starting on 14th June. It can be seen that the fertile days of the month are shown by the fertility indicator 264 as being 27th to 30th and 1st to 4th, which the user would understand to mean 27th June to 4th July, with the more fertile days of the month, indicated by crosses, being 28th to 30th and 1st to 3rd, which the user would take to mean 28th June to 3rd July. The days of the month on which the next period can be expected to start are shown by the start-of-next-period indicator 266 as being 16th and 17th, which the user would take to mean 16th and 17th July. [7] The embodiment of Figures 9 to 12 is identical to the embodiment of Figures 5 to 8 described above, except in the following respects. In Figures 9 to 12, features that are identical to or correspond to features in Figures 5 to 8 are referenced with reference numerals that are 100 greater than those in Figures 5 to 8, and features that are identical to or correspond to features in Figures 1 to 4 are referenced with reference numerals that are 200 greater than those in Figures 1 to 4. Referring to Figure 9, the start-of-last-period scale 130, its numbering 134 and its calibration instruction 138 are omitted, and the user does not mark the start-of-last period indicator. Instead, the start- of-last-period indicator 362 is pre-printed on the indicator slide 312 in a fixed position and subtends an angle P (i.e. 360/89°) at the centre of the hole 320. The fertility scale 340 has nineteen squares 342, with the first sequence of numbering 344 running from "22" to "34" starting at the anticlockwise end of the fertility scale 340, and the second sequence of numbering 346 running from "22" to "34" starting with the square numbered "28" in the first sequence of numbering 344. The calibration instruction 350 for the fertility scale 340 reads, for example, "Calibration: Mark the square on the left scale for your shortest cycle length, the scale on the right side for your longest cycle length and the squares in between." The start-of-next-period scale 352 has thirteen squares 354 numbered with a sequence of numbering 356 running from "22" to "34" starting at the anticlockwise end. The calibration instruction 360 for the start- of-next-period scale 352 reads, for example, "Calibration: Mark the squares for your shortest and longest cycle lengths and the squares in between." Each square 354 in the start-of-next-period scale 352 is angularly offset clockwise from the start-of-last-period indicator 362 by an angle N equal to the number of that former square multiplied by the angular pitch P. For example, the square 354 numbered "28" in the start- of-next-period scale 352 is angularly offset clockwise from the start-of-last-period indicator 362 by an angle N = (28x360)/89°. The squares 342 in the fertility scale 340 that are numbered by the first sequence of numbering 344 are angularly offset anticlockwise from the correspondingly numbered squares 354 in the start-of-next-period scale 352 by an angle Ol equal to nineteen times the angular pitch P, i.e. Ol = (19x360)/89°. The squares 342 in the fertility scale 340 that are numbered by the second sequence of numbering 346 are angularly offset anticlockwise from the correspondingly numbered squares 354 in the start-of-next-period scale 352 by an angle 02 equal to thirteen times the angular pitch P, i.e. 02 = (19x360)/89°. The instructions provided with the calculator 310 do not contain any instruction with regarding to calibrating any start-of-last-period scale. With regard to the fertility scale 340, the instructions state that the user needs (i) to mark the square 342 numbered in the first, left-hand sequence of numbering 344 with her shortest cycle length, (ii) to mark the square 342 numbered in the second, right-hand sequence of numbering 346 with her longest cycle length, and (iii) to mark each square 342 between those two squares 342, so as to form the fertility indicator 364. With regard to the start-of-next-period scale 352, the user needs (i) to mark the square 354 numbered with her shortest cycle length, (ii) to mark the square 354 numbered with her longest cycle length (if her variation is greater than zero days) and (iii) to mark each square 354 between those two squares 354 (if her variation is greater than one day), so as to form the start-of-next-period indicator 366. In the example shown in Figures 11 and 12, the indicator slide 312 has been calibrated for a woman having a shortest cycle length of twenty-four days and a longest cycle length of twenty-seven days. The instructions for use, each month, of the calculator 310 are similar to those for the calculator 110 of Figures 1 to 4, except that they omit to refer to any distinction between less fertile and more fertile days. In the example shown in Figure 12, the calendar slide 314 has been set relative to the indicator slide 312 for the case where the user's last period started on 29th January. Accordingly, the day-division 322 numbered "29" in the month-segment 328C for a 31 -day month on the calendar slide 314 has been aligned with the start-of-next-period indicator 362 on the indicator slide 112. In this position, the fertility indicator 364 on the indicator slide 312 is aligned with the day-divisions 322 numbered "3" to "12" on the calendar slide 114, and the user will understand that she can therefore expect to be possibly fertile between 3rd and 12th February. The start-of-next-period indicator 366 on the indicator slide 312 is aligned with the day-divisions 322 numbered "22" to "25" on the calendar slide 314, and the user will therefore understand that she can expect her next period to begin between 22nd and 25th March, if she has not fallen pregnant. Although complicating the instructions for calibration to some extent, the calculator 310 of Figures 9 to 12 can be used to draw a distinction between less fertile days and more fertile days. In this case, the instructions for calibration of the fertility scale 340 would state that the user needs (i) to mark a forward-slash in the square 342 numbered in the first, left-hand sequence of numbering 344 with her shortest cycle length, (ii) to mark a forward-slash in the square 342 numbered in the second, right-hand sequence of numbering 346 with her shortest cycle length, (iii) to mark a forward-slash in each square 342 between the squares 342 previously marked with forward-slashes, (iv) to mark a back-slash in the square 342 numbered in the first, left-hand sequence of numbering 344 with her longest cycle length, (v) to mark a back-slash in the square 342 numbered in the second, right-hand sequence of numbering 346 with her longest cycle length, (vi) to mark a back-slash in each square 342 between the squares 342 previously marked with back-slashes, and (vii) if there are any empty squares 342 between the squares 342 marked with back-slashes and forward- slashes, to mark a hyphen in each of those empty squares 342. In the example shown in Figures 9 to 12, the right-hand end of the fertility scale 340 abuts the left-hand end of the start- of-next-period scale 352 so that the scales 340,352 can have a maximum range without overlapping. However, if desired, a gap may be left between the scales 340,352, by omitting one of more of the squares and their numbering.

[8] The embodiment of Figures 13 to 17 is identical to the embodiment of Figures 9 to

12 described above, except in the following respects. In Figures 13 to 17, features that are identical to or correspond to features in Figures 9 to 12 are referenced with reference numerals that are 100 greater than those in Figures 9 to 12. The indicator slide 412 is not printed with a fertility scale 342, numbering 344,346 and instruction 350, nor with a start-of-next-period scale 352, numbering 356 and instruction 360. Instead it is printed with a series of thirteen, identically- shaped, numbered sticker outlines 470, and the calculator 410 is supplied with a sheet 472 of nine, correspondingly-shaped stickers 474A-I that are individually-removable from a backing sheet 475. The indicator slide 412 is circular having a diameter E of, for example, 180 mm. Referring to Figure 13, the sticker outlines 470 are angularly offset from each other by the angle P (i.e. 360/89°) around the centre of the hole 420. The outer corners of the sticker outlines 470 are numbered with sequences of numbering 476 running clockwise from "22" to "34". The sticker outline 470 numbered "26" has been emphasised in Figure 13 for clarity. The indicator slide 412 also bears a brief instruction 478 saying, for example, "Select sticker for your variation. Affix to disc in the outline for your shortest cycle length." Referring to Figure 15, the stickers 474A-I are provided one for each variation from zero days to eight days. Each sticker 474A-I is printed with a fertility indicator 464 and label 448, a start-of-next-period indicator 466 and label 458, and a sticker label 480, such as "Variation: 3 days", indicating the number of days variation for which that sticker 474A-I should be used. The positions and sizes of the fertility indicators 464 and start-of-next-period indicators 466 on the stickers 474A-I and the positions of the sticker outlines 470 on the indicator slide 412 are such that, when a sticker 474A-I for a particular variation is affixed to the indicator slide 412 aligned with the sticker outline 470 for a particular shortest cycle length, the fertility indicator 464 and start-of-next-period indicator 466 are appropriately positioned relative to the start-of-next-period indicator 462 and appropriately sized so as to perform a similar function to that described above with reference to Figures 1 to 12. It will be seen that the fertility indicators 464 for the stickers 474B-G for variations from 1 day to 6 days are stepped in height so as to distinguish between days when in- tercourse may, or may not, result in pregnancy depending on the current cycle length, and days when intercourse may result in pregnancy regardless of the current cycle length (provided that it is between the historic shortest and longest cycle lengths), as discussed above with reference to Figures 1 to 4. Also, instead of being stepped as shown, the heights of the fertility indicators 464 may increase progressively from minima at the ends of the fertility indicator 464 to a maximum at or adjacent the centre of the fertility indicator 464. Figure 17 shows the indicator slide 412 with the sticker 474D for a variation of three days affixed to the slide 412 in the sticker outline 470 for a shortest cycle length of 26 days. Figure 18 shows the indicator slide 412 and sticker 474D with the calendar slide 414 attached by the pop-stud 416 and set for a start- of- last-period date of 17th February. As can be seen, the fertility indicator 464 shows that intercourse between 24th and 5th (meaning 24th February to 5th March) may result in pregnancy, with the probability being greater from 27th February to 2nd March, and the start-of-next-period indicator 466 shows that the next period can be expected to start from 15th to 18th (meaning 15th to 18th March) if the user has not fallen pregnant. In the example shown in Figures 13 to 17, full outlines 470 have been marked on the indicator slide 412 for the stickers 474A-I. Alternatively, the indicator slide 412 may be marked with only the portions of the sticker outlines 470 that are covered by the calendar slide 414 once the calculator 410 is assembled, and the numbering 476 may be moved so that it lies under the calendar slide 414 once the calculator 410 is assembled, so that the indicator slide 412 appears uncluttered once the calculator 410 is assembled. In this case, an arc may be marked on the indicator slide 412 in the region of the sticker outlines 470 for alignment with marks printed on the edges of the stickers 474A-I to assist in correct positioning of the stickers 474A-I on the indicator slide 412.

[9] It will be noted that the calendar slide 114 described with reference to Figures 1 to 4 can cause an error of up to one day in the calculation of the fertile dates if 29th February in a leap year falls after the start date of the user's last period, but on or before her longest historic cycle length less thirteen days after the start date of her last period. Also, it will not be possible to set the slides 112,114 properly relative to each other if the start date of the last period is 29th February. In order to avoid these problems, Figure 18 shows a modified calendar slide 514 whose periphery is printed with a calendar scale having one hundred and eighteen day-divisions 522 at an angular pitch P of 360/118°. The calendar slide 514 is divided into four month- segments 524A-D by dividing lines 526. The month segments 524A-C are similar to the month- segments 124A-C described with reference to Figures 1 to 4, apart from the smaller pitch of the day-divisions 522, and the label 528C indicating that the month-segment 524C is for February in a non-leap year. The remaining month-segment 524D contains twenty-nine of the day-divisions 522 numbered "1" to "29" clockwise around the slide 514 and is printed with a label 528D indicating that it is for February in a leap year.

[10] It will be noted that the calendar slide 114 described with reference to Figures 1 to 4 can also cause errors in the calculation of the start dates of the next period if: (1) the longest cycle length is more than thirty days and the start of the last period is at the end of January, July or December; or (2) the longest cycle length is more than twenty-eight days and the start of the last period is at the end of April, June, September or November. In order to avoid such errors, Figure 19 shows a modified calendar slide 614 whose periphery is printed with a calendar scale having one hundred and fifty-one day-divisions 622 at an angular pitch P of 360/151°. The calendar slide 614 is divided into five month- segments 624A-E by dividing lines 626. The month-segment 624A contains thirty-one of the day-divisions numbered "1" to "31" and has a label 628A indicating that it is for use when the last period started in January. The next-clockwise month-segment 624B contains twenty-eight of the day-divisions numbered "1" to "28" and has a label 628B indicating that it is for use when the last period started in February. The next-clockwise month-segment 624C contains thiry-one of the day- divisions numbered "1" to "31" and has a label 628C indicating that it is for use when the last period started in March, May, August or October. The next-clockwise month- segment 624D contains thirty of the day-divisions numbered "1" to "30" and has a label 628D indicating that it is for use when the last period started in a thirty-day month or in April, June, September or November. The remaining month-segment 624E contains thirty-one of the day-divisions numbered "1" to "31" and has a label 628E indicating that it is for use when the last period started in July or December. The calendar scale 614 may be modified by alternatively disposing the month-segment 624E for July and December between the month- segment 624B for February and the month-segment 624C for March, May, August or October.

[11] It will be appreciated that the calendar scale 614 of Figure 19 can still cause the leap- year problem described with reference to Figure 18. In order to avoid both types of error, Figure 20 shows a modified calendar slide 714 which is printed with a calendar scale having two hundred and eleven day-divisions 722 at an angular pitch P of 360/211°. The calendar slide 714 is divided into seven month-segments 724A-G by dividing lines 726. The month-segment 724A contains thirty-one of the day-divisions 722 numbered "1" to "31" and has a label 728A indicating that it is for use when the last period started in January in a non-leap year. The next-clockwise month-segment 724B contains twenty-eight of the day-divisions 722 numbered "1" to "28" and has a label 728B indicating that it is for use when the last period started in February in a non-leap year. The next-clockwise month-segment 724C contains thirty-one of the day-divisions 722 numbered "1" to "31" and has a label 728C indicating that it is for use when the last period started in January in a leap year. The next-clockwise month- segment 724D contains twenty-nine of the day-divisions 722 numbered "1" to "29" and has a label 728D indicating that it is for use when the last period started in February in a leap year. The next-clockwise month-segment 724E contains thirty-one of the day-divisions 722 numbered "1" to "31" and has a label 728E indicating that it is for use when the last period started in March, May, August or October. The next- clockwise month-segment 724F contains thirty of the day-divisions 722 numbered "1" to "30" and has a label 728F indicating that it is for use when the last period started in a thirty-day month or in April, June, September or November. The remaining month- segment 724G contains thirty-one of the day-divisions 722 numbered "1" to "31" and has a label 728G indicating that it is for use when the last period started in July or December. The calendar scale 714 may be modified by alternatively disposing the month-segment 724G for July and December between the month-segment 724D for February in a leap year and the month-segment 724E for March, May, August or October. Also, the month-segments 724A,B for January and February in a non-leap year may be swapped with the month-segments 724C,D for January and February in a leap year.

[12] It should be noted that the calendar slide 714 of Figure 20 is designed to be the rear slide of the calculator and to be used with an indicator slide that is attached by the hole 720 over the calendar slide 714 and rotatable inside the calendar scale. The indicator slide may employ any of the techniques described above with reference to Figures 1 to 17. Also, any of the calculators 110,210,310,410 described with reference to Figures 1 to 17 may be modified so that the indicator slide 112,212,312,412 lies over the calendar slide 114,214,314,414 and is surrounded by the calendar scale. The calculators 110,210,310,410 described above may be modified to use ovulation intervals rather than cycle lengths as discussed in the introduction. In this case, the number 14 would be subtracted from the numbers in the numberings 134,234,344,346,356,476 described above, and the instructions would be amended to refer to ovulation intervals rather than cycle lengths. The calculators 110,210,310,410 described above may be used by a couple to assist in timing intercourse to promote pregnancy, or to assist in timing intercourse to avoid conception. In this latter contraceptive use, the calculator may be designed to account for a margin of error, for example by employing the assumptions that sperm lifespan is eight days, rather than five days, after intercourse and that egg lifespan is three days, rather than one day, after ovulation. Also, there is a slight possibility that intercourse between the fertile period indicated by the calculator and the start of the next period may result in conception, and the calculator may be marked to indicate that possibility. It should be noted that the embodiments of the invention have been described above purely by way of example, and that many other modifications and developments may be made thereto without departing from the scope of the invention.

Claims

[1] A conception calculator (110;210;310;410) in the form of a circular slide rule comprising a calendar slide (114;214;314;414;514;614;714) and an indicator slide (112;212;312;412) arranged for relative rotation, wherein: the calendar slide has a continuous circular calendar scale; the calendar scale is divided into a plurality of equiangularly-pitched day-divisions (122;222;322;422;522;622;722); the calendar scale is also divided into at least three labelled month-segments (124A-C; 424A-C;524A-D;624A-E;724A-G), each month-segment containing a number of the day-divisions equal to the number of days in a particular calendar- month or group of calendar- months; the indicator slide is marked with, or is set out to be marked with, a fixed start-of-last-period indicator (162;262;362;462), which a user can, upon relative rotation of the slides, align with that one of the divisions of the calendar scale corresponding to the date of the start of her last period; the indicator slide is set out to be marked with a fixed fertility indicator (164;264;364;464) which is angularly offset from the start-of-last-period indicator and which, when the start-of-last-period indicator is so aligned, indicates on the calendar scale a sequence of days-of-the-month when the user can expect to be fertile; and the angular offset of the fertility indicator from the start-of-last-period indicator and the number of days in the sequence indicated by the fertility indicator are both arranged to be determined in dependence upon the values of two numeric parameters related to the user's menstrual cycle history.

[2] A calculator (110;210) as claimed in claim 1, wherein: the indicator slide

(112;212) is set out to be marked with the start-of-last-period indicator (162;262) in dependence upon the value of one of the numeric parameters; and the indicator slide is set out to be marked with the fertility indicator (164;264) in dependence upon the value of the other of the numeric parameters.

[3] A calculator as claimed in claim 2, wherein: the indicator slide (112;212) bears a numbered scale (130;230) set out to be marked in dependence upon the value of said one numeric parameter in order to provide the start-of-last-period indicator; and the indicator slide bears another numbered scale (140;240) set out to be marked in dependence upon the value of said other numeric parameter in order to provide the fertility indicator.

[4] A calculator as claimed in claim 2 or 3, wherein the indicator slide is partly marked in one manner and is set out to be marked in a different manner in dependence upon the value of said other numeric parameter in order to provide the fertility indicator.

[5] A calculator (310;410) as claimed in claim 1, wherein: the indicator slide (312;412) is marked with the start-of-last-period indicator (362;462); and the indicator slide is set out to be marked with the fertility indicator (364;464) in dependence upon the values of both numeric parameters.

[6] A calculator (310) as claimed in claim 5, wherein the indicator slide (312) bears at least one numbered scale (340) set out to be marked in dependence upon the values of both of the numeric parameters in order to provide the fertility indicator (364).

[7] A calculator as claimed in claim 6, wherein the indicator slide is set out to be marked in one manner in dependence upon the value of one of the numeric parameters and in a different manner in dependence upon the value of the other numeric parameter in order to provide the fertility indicator.

[8] A calculator (410) as claimed in claim 5, wherein: the indicator slide (412) is marked with a plurality of label positions (470) for different values of one of the numeric parameters; and the calculator is provided with a set (472) of labels (474A-I) each bearing such a fertility indicator (464) for a respective value of the other numeric parameter; whereby such a label can be selected in dependence on the value of said other numeric parameter and affixed to the indicator slide in a position in dependence upon the value of said one numeric parameter in order to provide the fertility indicator on the indicator slide.

[9] A calculator as claimed in claim 8, wherein the fertility indicator on each label is arranged to indicate different probabilities of fertility for different days in dependence upon the respective value of said other numeric parameter.

[10] A calculator as claimed in any preceding claim, wherein: the indicator slide is set out to be marked with a fixed start-of-next-period indicator (166;266;366;466) which is angularly offset from the start-of-last-period indicator and which, when the start-of-last-period indicator is so aligned, indicates on the calendar scale a day-of-the-month or sequence of days-of-the-month when the user can expect her next period to start if she has not fallen pregnant; and the angular offset of the start-of-next-period indicator from the start-of-last-period indicator and the number of days indicated by the start-of-next-period indicator are both arranged to be determined in dependence upon the values of both of the numeric parameters.

[11] A calculator as claimed in claim 10 when directly or indirectly dependent on claim 2, wherein the indicator slide bears a numbered scale (152;252) set out to be marked in dependence upon the value of said other numeric parameter in order to provide the start-of-next-period indicator (166;266).

[12] A calculator as claimed in claim 10 when directly or indirectly dependent on claim 6, wherein the indicator slide bears a numbered scale (352) set out to be marked in dependence upon the values of both of the numeric parameters in order to provide the start-of-next-period indicator.

[13] A calculator as claimed in claim 10 when directly or indirectly dependent on claim 8, wherein: each label bears such a start-of-next-period indicator (466) dependent on the value of said other numeric parameter for that label; whereby when such a label is selected in dependence on the value of said other numeric parameter and affixed to the indicator slide in the position in dependence upon the value of said one numeric parameter, the label provides the start- of-next-period indicator on the indicator slide.

[14] A calculator as claimed in any preceding claim, wherein the numeric parameters are: shortest and longest cycle lengths; or shortest cycle length and variation in cycle lengths; or longest cycle length and variation in cycle lengths.

[15] A calculator as claimed in any of claims 2 to 4, 7 to 9, 11 and 13, wherein said one numeric parameter is shortest cycle length and said other numeric parameter is variation in cycle lengths.

[16] A calculator as claimed in any of claims 1 to 13, wherein the numeric parameters are: shortest and longest ovulation intervals; or shortest ovulation interval and variation in ovulation intervals; or longest ovulation interval and variation in ovulation intervals.

[17] A calculator as claimed in any of claims 2 to 4, 7 to 9, 11 and 13, wherein said one numeric parameter is shortest ovulation interval and said other numeric parameter is variation in ovulation intervals.

[18] A calculator as claimed in any preceding claim, wherein there are between three and seven of the month-segments.

[19] A conception calculator (110;210;310;410) in the form of a circular slide rule comprising a calendar slide (114;214;314;414;514;614;714) and an indicator slide (112;212; 312;412) arranged for relative rotation, wherein: the calendar slide has a continuous circular calendar scale; the calendar scale is divided into a plurality of equiangularly-pitched day-divisions (122;222;322;422;522;622;722); the calendar scale is also divided into between three and seven labelled month- segments (124A-C;424A-C;524A-D;624A-E;724A-G), each month-segment containing a number of the day-divisions equal to the number of days in a particular calendar- month or group of calendar- months; the indicator slide is marked with, or is set out to be marked with, a fixed start-of-last-period indicator (162;262;362;462), which a user can, upon relative rotation of the slides, align with that one of the divisions of the calendar scale corresponding to the date of the start of her last period; and the indicator slide is marked with, or set out to be marked with, a fixed fertility indicator (164;264;364;464) which is angularly offset from the start-of-last-period indicator and which, when the start- of-last-period indicator is so aligned, indicates on the calendar scale a sequence of days-of-the-month when the user can expect to be fertile.

[20] A calculator as claimed in claim 18 or 19, wherein there are seven such month- segments (724A-G) consisting of: (i) a first month-segment (724A) containing thirty-one of the day-divisions (722) for the month of January in a non-leap year; (ii) a second month-segment (724B), immediately after the first month segment, containing twenty-eight of the day-divisions for the month of February in a non- leap year; (iii) a third month-segment (724C) containing thirty-one of the day- divisions for the month of January in a leap year; (iv) a fourth month-segment (724D), immediately after the third month segment, containing twenty-nine of the day-divisions for the month of February in a leap year; (v) a fifth month- segment (724F) containing thirty of the day-divisions for the months of April, June, September and November; (vi) a sixth month-segment (724E), immediately before the fifth month- segment, containing thirty-one of the day-divisions for the months of March, May, August and October; and (vii) a seventh month-segment (724G), immediately before the first, third or sixth month-segment, containing thirty-one of the day-divisions for the months of July and December, so that there are two hundred and eleven such day-divisions in total.

[21] A calculator as claimed in claim 18 or 19, wherein there are five such month- segments (624A-E) consisting of: (i) a first month-segment (624A) containing thirty-one of the day-divisions for the month of January; (ii) a second month- segment (624B), immediately after the first month segment, containing twenty- eight of the day-divisions for the month of February; (iii) a third month-segment (624D) containing thirty of the day-divisions for the months of April, June, September and November; (iv) a fourth month-segment (624C), immediately before the third month-segment, containing thirty-one of the day-divisions for the months of March, May, August and October; and (v) a fifth month-segment (624E), immediately before the first or fourth month-segment, containing thirty- one of the day-divisions for the months of July and December, so that there are one hundred and fifty-one such day-divisions in total.

[22] A calculator as claimed in claim 18 or 19, wherein there are four such month- segments (524A-D) consisting of: (i) a first month-segment (524A) containing thirty-one of the day-divisions (522) for the months of January, March, May, July, August, October and December; (ii) a second month-segment (524B) containing thirty of the day-divisions for the months of April, June, September and November; (iii) a third month-segment (524C) containing twenty-eight of the day-divisions for the month of February in a non-leap year; and (iv) a fourth month- segment (524D) containing twenty-nine of the day-divisions for the month of February in a leap year, so that there are one hundred and eighteen such day-divisions in total.

[23] A calculator as claimed in claim 18 or 19, wherein there are three such month- segments (124A-C) consisting of: (i) a first month-segment (124A) containing thirty-one of the day-divisions (122) for the months of January, March, May, July, August, October and December; (ii) a second month-segment (124B) containing thirty of the day-divisions for the months of April, June, September and November; and (iii) a third month-segment (124C) containing twenty-eight of the day-divisions for the month of February, so that there are eight-nine such day-divisions in total.

[24] A calculator as claimed in any preceding claim, wherein every day-division is so numbered.