WO1989003502A2

WO1989003502A2 - Improvements in and relating to scale rules

Info

Publication number: WO1989003502A2
Application number: PCT/GB1988/000873
Authority: WO
Inventors: Anthony Richard Johnson
Original assignee: Anthony Richard Johnson
Priority date: 1987-10-16
Filing date: 1988-10-17
Publication date: 1989-04-20
Also published as: GB9005974D0; GB2229525B; WO1989003502A3; GB2229525A; GB8724332D0

Abstract

In aiming to produce scale rule apparatus which is simple to use avoiding known computer based systems or the need to perform manual calculation on scale lengths, and yet to arrive at a conversion device which is accurate, the present invention provides scale rule apparatus comprising a self-contained (portable) electronic processing unit which receives scale length signals from a measuring wheel and automatically calculates and displays the actual length according to the selected scaling factor. Signal transmission from the measuring wheel to the processing unit is improved by filtration and amplification in the measuring wheel and resolution of the input signal is enhanced by use of processing techniques which respond to both positive and negative changes of state of the signal pulse.

Description

Title: Improvements in and relating to scale rules.

DESCRIPTION

The present invention relates to a scale rule, primarily a counting and scaling device, also to take off devices for use with same, including a take off probe and a measuring wheel, and to improvements in handling signals from such take off devices.

It is frequently necessary to measure off drawings - usually scale drawings, lengths of items, for the purpose of ordering quantities of materials.

In making such measurements an electronic measuring wheel is run along/over the part whose length is to be calculated, with the data being fed into a computer which has instructions on floppy discs or magnetic tape to facilitate conversion of the reading taken from the drawing into actual lengths. The discs or tape stores the instructions when the machine is turned off and allows the operator on start up of the machine to load the instructions and select the conversion scale which is to be applied to the incoming data.

The requirement for a computer with disc or tape drive for storing the conversion instructions makes the apparatus bulky and not readily portable thereby restructing its use to the location of the equipment.

It is an aim of the present invention to provide a device to assist and speed up the generation of an accurate take off from scaled drawings to facilitate the quantification of cables, conducts, pipes etc. without- using a mechanical scale rule, pencil and paper. It is a further aim to provide a scale rule which is self contained and preferably readily portable for performing such calculations automatically without the need to load operating- instructions.

Accordingly, one aspect of the present invention provides a scale rule comprising a self contained electronic processing unit having an input which receives scale length signals from a measuring wheel, selectable scaling means operable on said input for calculating actual lengths, and display means for the calculated output. We find it particularly advantageous to have a plurality of preset scales corresponding to popular scales used in metric and imperial drawings, and we find it especially convenient to have a separate actuable key for each preset scale. Using micro chip technology the relevant instructions for conversion can be held even with loss of power to the device. Moreover, the use of micro chips allows the use of any scaling factor be it part or whole number conversions, and we also propose to incorporate automatic conversion from imperial to metric units.

We propose a machine of a portable nature - certainly no larger than a desk top calculator - and to arrange the circuitry such that when switched on selection of the appropriate scale key results in automatic conversion of any input signal from the electronic measuring wheel to actual length measurement.

In fact we prefer to have the actual calculated value display in metric units, although we do not rule out optional selection of metric or imperial units and/or facility to convert from one to the other at the press of a button - again using pre-programmed micro chips. By producing a device with particular emphasis on the calculation of lengths, the instructional information required to convert signals of scale length can be incorporated into the electronics so as to be performed automatically, with the operator simply selecting, preferably prior to operating the electronic measuring wheel, the scale of the drawing from which measurements are being taken. Using separate keys for each preset scale enables this to be done by operation of a minimum number of keys/keying operations.

Of course we also provide for performing calculations on the calculated lengths using a conventional calculator key board entry pad to allow for multiplications, division, addition or subtraction. We also prefer to have an input for receiving signals from an electronic incrementing probe which is used to count numbers of items, each operation of the probe serving to increment the output by 1 normally on an additional basis, but optionally selectively as subtraction, multiplication or division. Such accummulated values can also be operated on from the keyboard input of the device.

Whilst individual keys for each scale are preferred, it is also feasible for a single key to select one of a number of preset scales by indexing through same. Advantageously an output display shows the scale selected.

Since drawings follow conventional scales by and large we find that 10 preset scales are sufficient to cover all the conventional scales in common use. However, it may be advantageous for the device to include a programmable memory by means of which a non-standard scale may be set up to give automatic conversion.

We prefer to incorporate a printer in the device to output hard copy of calculated values. Such counting and scaling apparatus for use in measuring lengths from scale drawings and for counting/marking numbers of items, calls for a measuring wheel for the former and a take off probe for the latter. Take off probes and measuring wheels (referred to generally as take off devices) are already known, but known take off probes which utilise an electrical contact can give eroneous signals due to contact bounce, and in the case of measuring wheels utilising light making breaking techniques, existing designs are expensive to construct to achieve the desired accuracy. Furthermore, the construction of the known devices renders the generated signal susceptable to interference on transmission to the scale conversion unit. Accordingly it is a further aim of the present invention to provide, for such a scaling and counting apparatus, an improved take off device, (probe and/or measuring wheel), and in the case of the latter to provide for improved accuracy/signal handling. Accordingly, the present invention provides a take off device for use with a scaling and/or counting apparatus in which light emitter and detector means is provided to generate a pulsed electrical signal responsive to operation of the device for input to the scaling/counting apparatus and wherein the device incorporates integral electronics which filter and/or amplify the signal before transmission to the scaling/counting apparatus.

By this means the transmitted signal is much less susceptable to interference. The take off device may be such as a take off probe for counting purposes or a measuring wheel for length measurement (such as described herein). The light emitter and detector means is conveniently a light emitting diode and photo-detector, preferably operating on infra-red light, although other wavelengths may be preferred beit visible or non-visible. The take off device is conveniently connected to the scaling/counting device by electric wires providing required power voltage and signal output, although the former could be from a self contained power source in the probe, whilst signal transmission could be wireless.

Preferred electronics in the probe include a schmitt trigger for filtration and an amplifier, also for convenience a voltage regulator. According to a further aspect of the present invention then there is provided a take off probe for use with counting/computing apparatus, comprising a carrier receiving slidably take-off means which is actuable for reciprocal movement relative to the carrier against a biasing force and has means to break and make light transmission between light (preferably infra-red) emitter and detector means within the body to thereby generate a signal pulse responsive to actuation of the take off means against the biasing force.

The take off probe may incorporate the aforementioned integral electronics.

The take off means conveniently has an elongate body of which part is accommodated within the carrier, and part projects permitting actuation for counting purposes. More particularly, the take off probe carries marker means, and a particularly convenient construction results where take off means is formed by a marking device, such as ball point pen or marker pen refil. The end of the take off probe is conveniently employed as the means for breaking and making light transmission. The end may be the end of the aforementioned refil or a shutter device actuated thereby. Producing a measuring wheel using light making/breaking techniques to generate a signal on rotation of such as an apertured wheel (say spoked) requires accurate production of the spokes at equally spaced intervals. In practice we found this became more difficult as the number of spokes increased, whilst the use of traditional counting techniques in which a photo-detector simply increments a counter in response to absence or more usually presence of light (hence signal) gave results which highlighted discrepancies in accuracy. With mechanical counters there was a problem with repeatability, and often giving different results for forward and backward running of the wheel along a given line. A yet further aspect of this invention is aimed at providing scaling apparatus which overcomes that problem.

According to that yet further aspect there is provided a means of enhancing the resolution of a length measuring device which device comprises a wheel having a configuration, such as radial spokes, which makes and breaks light transmission between light emitter and detector means to generate a signal pulse on rotation of the wheel, wherein resolution is enhanced by electronic circuit means detecting change of signal state so as to generate a pulse count for both light transmission and light interruption. By this means the resolution of the measuring wheel is doubled, making it possible, for example, for a six spoke design to produce a pulse frequency equivalent to that of a twelve spoke design. The preferred measuring wheel has a wheel with six spokes positioned to interupt the beam of light between an infra red emitter and detector. More preferably, the spoked wheel is rotated by a driving wheel using gears, which driving wheel is run along the length to be measured. The geared arrangement allows for the driving wheel to be of sufficiently large diameter, and in that regard we find it advantageous to use a wheel about the same size as the body of the device, 14 mm diameter in our preferred embodiment, whilst the spoked wheel can be smaller to be accommodated within the body and geared up to rotate faster than the driving wheel for added accuracy.

The various aspects of the present invention will now be described further hereinafter, by way of example only, with reference to the accompanying drawings; in which:

Figure 1 illustrates the layout of a device according to the invention together with sample input probes; Figures 2 and 3 show sectional views at 90 degrees of a take off probe;

Figures 4 and 5 show sectional views at 90 degrees of a measuring wheel; Figure 6 illustrates the infra red emitter and detector circuitry for a take off probe or a measuring wheel; and

Figure 7 illustrates in block diagram form the resolution enhancement system. Referring firstly to Figure 1 there is shown an electronic scale rule housed in a casing 100 which is generally of the size of a desk top calculator or office telephone and has inputs 103, 105, of plug-in type, for a measuring probe 107 and a take-off probe 109 - connected by respective leads - say 2 m or so in length. A display, typically using a liquid crystal read out (but could be L.E.D.) is shown at 111 and additionally a printer 113 is provided for hard copy of the output onto paper 115. A first key pad 117 has preset keys for scale (ten in the illustration) plus a scale on/off key 119 and a scale select key 121. Four imperial and six metric scales, those commonly used, are illustrated. The device is programmed to automatically convert input signals from imperial drawings when an imperial scale is selected to display actual lengths in metric.

An L.E.D display or otherwise is provided at 123 to indicate the scale selected. As an alternative the keys themselves may give a visual indication when selected. A ten digit key pad is illustrated at 125 plus two additional special function keys 27, 29 whose function will be described further hereinafter. Standard function keys plus cancel and cancel entry keys are shown in two vertical rows at 131 towards the right hand of the device. There is also a selection key 132 for decimal point selection allowing floating, none, two, three or four places of decimals.

The use of a measuring probe provides a particularly advantageous system. It is basically a marking pen 133 with counting wheel 135 attached, similar but scaled down in size to the measuring wheels used for roadworks. The measuring probe will perform a similar function to a map measurer used in geography.

Another embodiment of probe is described further hereinafter. The measurer will have a set scale e.g. one revolution of the wheel equals ten metres on the drawing. When an alternative scale is selected, say

1:100, each revolution of the wheel is to be multiplied by ten, and each port ion of a revo lut ion to be mult ip l ied with the same ratio. The same shall apply to each scale selected.

If a scale of 1/8-1 foot is selected this would represent 1:96 in metric terms and the suitable conversion applied from a solid state memory bank_* A small tone generator (optional) is to indicate a tone as the probe is measuring off the drawing. This is to indicate to the operator that the probe is registering the measurement in the machine.

It is preferred that the probe register into the machine when the wheel is turned, preferably with means to prevent accidental input, such as by switching, such as by operation of the select on/off key or some other key to signal that readings are to be input, although any other switching available selecting technique may be used. The aim is to avoid accidental entry into the machine by the wheel 135 being knocked or turned accidentally. The wheel is to add if run backwards or forwards, and only to subtract if the minus is pressed on the mode function 131. Basically, the wheel operates a make and break contact to give signal pulses as it rotates which signals are accurately related to distance travelled. Only the entry from the measuring wheel is to be affected by the scale selections.

An entry from the measuring wheel may be added to, subtracted from, divided or multiplied by a selection from the mode keys 131,125 although generally we find that the measuring wheel take off need only be affected by scale selection and plus and minus keys of the mode selection. This will enable the operator to measure a cable or pipe etc., and run over the same run in the minus mode if he wishes to subtract a previous entry.

The marker 133 may be a pencil lead grab mechanism, similar to that of a propelling pencil, but any other convenient marking means may be employed. This will enable different runs of pipes, conduits, cables etc., to be identified with different coloured leads.

The take off probe 9 is basically a pen 137 with a spring loaded contact within the pen. Each time the contact is made a unit of One is entered on the display. An entry from the take off probe 109 will automatically add to or subtract from the total on the display, as selected from the mode keys. This probe can be used to count individual items (e.g. switches, sockets, light fittings, sink units, taps, drains, elbows etc......). The advantage of providing a pen with the contact is that items may be marked off on a drawing as they are counted. Each entry is to be accompanied with one note of the tone generator. This will let the operator know the entry has been accepted.

On the illustrated model it is permissable to select six forms of metric scale and four forms of imperial scale. If the metric or imperial scales are chosen the end result is to give a measurement in metres and decimals of metres only. This may be added to, subtracted from, divided or multiplied by using the key board. To select a scale press SCALE SELECT (key 121) and then the scale required (one of keys 117). When using the measuring probe 107 select scale ON/OFF (key 119) and the selected scale will show itself on the scale selection section of the read out. The scales selection mode is to operate only with the measuring probe. The keys and take off probe are not to be affected by scale selection. To give printed information of calcuation or measurement if required, the printer may be turned on or off by switch 39 above mode of operation buttons (117).

The machine may be used as a calculator or measuring instrument as required. As a normal calculator, any entry may be multiplied, divided, added or subtracted. This is to include any entry from the take off and measuring probes (109, 107). The machine will have the facility to enter a figure on the key board, press the plus, minus, divide or multiply key, using the take off or measuring probes enter a figure and continue to add or subtract etc.... from either keys, take off, or measuring probes.

The probes may be used as an extension to the key board.

On completion of a measurement or an addition, pressing enter will store the total in a memory and if in use, print the figure on the paper roll. If several items of the same manufacture are being measured (e.g. 20mm electrical conduit). Several different measurements can be obtained for different rooms or circuits and a complete total given on completion by pressing the * key 129.

Key C will cancel all previous entries and calculations and return the machine to accept new instructions. Key CR will cancel the last digits mistakenly keyed in. The equal key is to be used on completion of a multiplication or division. After the key is pressed the figure is ready for addition, subtraction or enter. The position of Key 33 determines if the decimal point should remain for whole numbers only, round off to 2,3, or 4 decimal points, or remain floating as the calculations determine. Referring now to Figures 2 and 3, there is illustrated a take-off probe comprising a body 5, hollow and cylindrical in the illustrated embodiment, and take-off means 7 slidably guided for movement relative to the body 5 and received within the body save for one end 9 which passes through a nozzle 11 located at one end of the body 5. The take-off means is moveable slidably between and extended position, with the end 9 projecting furthermost from the nozzle, and a depressed position against the action of a spring 13. The spring engages with a flange 15 held relative to the body.

In the illustrated embodiment the spring engages a sleeve-like carrier 25 which fits over the end of the take-off probe, actually apertured at 26 to receive the end 28 of the take-off probe and seal on a shoulder 30. The carrier has a rim 27 which provides sliding engagement with the inner bore of the body 5, and an actuator recess 29 which receives the spring 13. The flange 15 is formed by the end of a tubular sleeve 17 of plastics received within the body from the end opposite to the nozzle 11. The sleeve accommodates an infra-red light emmiter device 19 and an infra-red light detector device 21 disposed opposite one another and spaced apart. A sheathed cable 23 leads into the sleeve and provides wiring connections to the emmiter and from the detector. The flange is operated for passage therethrough of the end 28 of the take-off probe.

In operation, holding the body 5 and contacting the end 9 with a surface causes the take-off means to be moved from its extended position against the spring biasing force, and for the end 28 to be positioned between the infra-red emmiter and detector so excluding the passage of light therebetween to generate a change of signal as described further hereinafter. The spring bias returns the take-off probe to its extended position when pressure on the body is released.

The function of the take-off probe is to count numbers of items from such as a scale drawing of plant. It is useful if that counting is accompanied by physical marking-off a checking-off of all items counted and this can be achieved readily with the take-of f probe of the present invent ion by having the take-off means constructed as a marker device, with the end 9 constituing a marking or writing tip. In the preferred embodiment the take-off probe comprises a ball-point pen refil or the like.

Referring now to Figures 4 and 5, here there is illustrated a measuring wheel device for measuring dimensions off scale drawings, and for use in converting to actual dimensions of materials for ordering lengths, areas, or volumes of materials. The device comprises a body 35, typically as a hollow cylindrical tube, carrying a take-off wheel 37 journalled for rotation in a carrier 38 received in an end of the body. The take-off wheel 37 is run along dimensions to be measured and drives a counting wheel 39 by way of a geared connection. The outer periphery of wheel 37 is toothed to cooperate with a gear wheel 41 coaxial with the wheel 39 and fixed relative thereto. The wheels 39 and 41 we journalled for rotation in the carrier 39.

The counting wheel 39 has six radial spokes 43 disposed equally spaced around the wheel and each separated by a gap. The spokes and gaps each have equal dimensions for reasons which will be apparent hereinafter.

The device also has a light emitting device 45 and a light detecting device 47 located within the carrier and spaced apart for passage therebetween of the spokes 43 of wheel 39 on rotation thereof. Rotation of the wheel gives alternating transmission and occlusion of light between the emitter and detector. Using appropriate electronic circuitry, as illustrated with reference to Figures 6 and 7, a pulsed signal is generated. Wiring for the emitter and detector means is shown at 49 and passes out of end cap 51 for connection to the counting device. I have found that a take-off wheel diameter of 14 mm driving through a 3.73 mm diameter gear wheel 41 and utilising a 10 mm diameter counting wheel, giving a gear ratio of 3.75=1 gives 47-48 counts per revolution equal to 45 mm. Referring now to Figure 6, there is shown the circuit diagram for the emmiter and dectector devices as used in the take-off probe and the measuring wheel device. The emitter comprises on L.E.D 61 gving off infra red light and the detector comprises a photo diode 63. An amplifier 65 increases signal level whilst a schmitt trigger 67 cleans up the resulting pulse form to a square wave (with transistor 69) and providing a signal or no signal at desired level (actually 5V and OV in the preferred embodiment) for input to the counting stage. The circuitry also includes a voltage regulator 70 to which a 5V input line is connected. The circuitry of Figure 6 is provided within the body of the probes .

By means of the circuitry, the signal from the detector is filtered by the action of the Schmit trigger (or equivalent) before being amplified to increase the signal level and before being sent down a cable linking the probe(s) to the scaling device. This makes the transmitter signal much less susceptable to intereference.

Figure 7 shows in block diagram from the hardware and software functions required to take inputs from either a take-off probe 80 or a measuring wheel 82 and produce an appropriate display. Dotted line 84 marks the division between circuitry external (above) and internal (below) to scale rule/counting apparatus with software functions identified by box 86 and the various hardware devices identified separately, namely display 88, printer 90, mode switch 92 and keypad 94. Signal received from the probe or wheel is bufferred and filtered by way of filter and 2nd Schmitt trigger (79, 81; 79', 81'). The noise free signal is fed to the following circuitry. For the take-off probe, input to the scale rule/counting apparatus is in the form of a pulse signal corresponding to transmission and interruption of light, with one or the other being required to be noted to count items being checked off. For this purpose the software operates with a counter or interrupt register 100 and signals from the counter are operated on by input from the keypad 94 in conjunction with calculator/microprocessor 102 with the results being output to display. Mode selection switch 92 conditions the calculator to accept input from the take-off probe or the measuring wheel probe by way of the mode selection software.

In the case of the measuring wheel device, the noise free signal from the device is again in the form of a pulsed signal arising from transmission and occlusion of light and is fed to a following circuit 106. The device/software incorporates provisions for enhancing the resolution of the measuring wheel

(actually doubling it compared with traditional measuring techniques) and this is done by providing for count on change of state using a change of state detector 106 in which the circuit interrupts the computer on both positive and negative state transitions. In conjunction with interrupt register

108 this serves to create a count as the signal from the measuring wheel changes state, i.e. on change from say 0 volts to 5 volts and back from 5 V to 0 V. In effect then the software takes account of both the transmission and occlusion of light so effectively doubling the number of count for a given number of spokes on the wheel. By this means a six spoke counting wheel can be made to give the same resolution as a twelve spoke wheel.

The resulting signal is passed to the calculation software for conversion to actual lengths according to the scale selected using the mode section switch 92 via software 104 and scale buttons, also allowing calculations to be performed thereon. More particularly, for each interrupt cycle the computer 102 increments a software counter, in such a way that a tally is held which represents the number of beam interruptions and transmissions. As the distance that the probe has to travel in order to interrput the beam is the same distance that the probe has to travel in order to cause the beam to be transmitted, the electronics effectively doubles the accuracy of the measuring system. The count held by the operation of the interrupt routine is proportional to the number of hole widths traversed by the probe.

This count is displayed by the software in different ways depending on the last "SCALE" button pressed in such a way as to electronically emulate a physical "scale rule". In operation the first count is multiplied by a conversion factor applied from each scale selection. The next count is also multiplied by the selected conversion factor and added to the previous figure and displayed on the L.C.D. The third count is multiplied by the conversion factor and added to the sum of the previous counts and then displayed on the L.C.D. The same formula is then applied to all subsequent counts and then L.C.D. is continually updated and displayed.

The conversion to actual lengths is performed automatically having preselected the scale from which measurments are taken as described above in relation to Figure 1 for which the abovedescribed take-off probe and measuring wheel device and the resolution enhancement system are intended for use, usually being provided as part of a package.

International Bureau

INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)

(51) International Patent Classification ⁴ : (11) International Publication Number : WO 89/ 035

G01B 3/12; G01D 5/34; G06M 1/10; A3 B43K 8/00, 29/08 (43) International Publication Date : 20 April 1989 (20.04.

(21) International Application Number : PCT/GB88/00873 HU, IT (European patent), JP, KP, KR, LK, LU ( ropean patent), MC, NL (European patent), NO, R

(22) International Filing Date: 17 October 1988 (17.10.88) SD, SE (European patent), SU, US.

(31) Priority Application Number: 8724332

Published

(32) Priority Date: 16 October 1987 (16.10.87) With international search report

Before the expiration of the time limit for amending t

(33) Priority Country: GB claims and to be republished in the event of the receipt amendments.

(71)(72) Applicant and Inventor: JOHNSON, Anthony, Ri(88) Date of publication of the international search report: chard [GB/GB]; 33 Princes Avenue, Crosby, Mersey- 18 May 1989 (18.05.8 side L23 5RR (GB).

(74) Agent: ROYSTONS; Tower Building, Water Street, Liverpool L3 1BA (GB).

(81) Designated States: AT (European patent), AU, BB, BE (European patent), BG, BR, CH (European patent), DE (European patent), DK, FI, FR (European patent), GB, GB (European patent),

(54) Title: IMPROVEMENTS IN AND RELATING TO SCALE RULES

.105

70

VOLTAGE REGULATOR

SCHMITT TRIGGER

B9|

^67

AMPLIFIER

5 v V+ Vc SIGNAL RETURN

(57) Abstract

In aiming to produce scale rule apparatus which is simple to use avoiding known computer based systems or th need to perform manual calculation on scale lengths, and yet to arrive at a conversion device which is accurate, the presen invention provides scale rule apparatus comprising a self-contained (portable) electronic processing unit which receive scale length signals from a measuring wheel and automatically calculates and displays the actual length according to th selected scaling factor. Signal transmission from the measuring wheel to the processing unit is improved by filtration an amplification in the measuring wheel and resolution of the input signal is enhanced by use of processing techniques whic respond to both positive and negative changes of state of the signal pulse.

FOR THE PURPOSES OFINFORMAHON ONLY

Codes used to identify States party to the PCT on the front pages of pamphlets pubh^'shing international applications under the PCT.

AT Austria FR France ML Mali

AU Australia GA Gabon MR Mauritania

BB Barbados GB United Kingdom MW Malawi

BE Belgium Hϋ Hungary L Netherlands

BG Bulgaria IT Italy O Norway

BJ Benin JP Japan RO Romania

BR Brazil KP Democratic People's Republic SD Sudan

CF Central African Republic of Korea SE Sweden

CG Congo KR Republic of Korea SN Senegal

CH Switzerland LI Liechtenstein su Soviet Union

CM Cameroon LK Sri Lanka TD Chad

DE Germany, Federal Republic of LU Luxembourg TG Togo

DK Denmark MC Monaco US United States of America

FI Finland MG Madagascar

Claims

1. Scale rule apparatus comprising a sel f contained electronic processing unit having an input which receives scale length signals from a take off device in the form of a measuring wheel, selectable scaling means operable on said input to calculate actual length automatically on receiving scale length signals according to the scale selected, and display means for the calculated output.

2. Scale rule apparatus as claimed in claim 1 in which the selectable scaling means comprise a plurality of preset scales selected by an actuable key.

3. Scale rule apparatus as claimed in claim 1 or 2 further comprising a calculator key board entry pad for performing calculations on the calculated scale lengths.

4. Scale rule apparatus as claimed in claim 1, 2 or 3 in which the take off device uses light emitter and detector means to generate the scale length signals independence upon rotation of the wheel, and wherein the device incorporates integral electronics which filter and/or amplify the signal before transmission to the processing unit.

5. Scale rule apparatus as claimed in claim 4 in which the integral electronics include a schmitt trigger for filtration and an amplifier.

6. Scale rule apparatus as claimed in any one of claims 1 to 5 in which the resolution of the take off device (e.g. measuring wheel) producing scale length signals in response to operation of light emitter and detector means is enhanced by electronic circuit means which detects change of signal state so as to generate a pulse count for both light transmission and light interruption.

7. Scale rule apparatus as claimed in any preceding claim in which the measuring wheel has six equally spaced radial spokes positioned to interrupt a beam of light between infra-red emitter and detector means, with spokes and spaces of equal size.

8. Scale rule apparatus as claimed in any preceding claim in which the take off device is connected to the processing unit by a flying lead.

9. A method of calculating scale lengths using a portable self contained scale rule apparatus and a measuring wheel generating scale length signals for input into the scale rule apparatus, the method comprising activating the scale rule apparatus, selecting from available pre-set scales the scale factor to be applied to the incoming scale lengths and running the measuring wheel over the lengths to be measured with the actual length being automatically calculated and displayed.

10. A take off device for use with a scaling and/or counting apparatus, in which light emitter and detector means is provided to generate pulsed electrical signals responsive to operation of the device for input to the scaling/counting apparatus, and wherein the device incorporates integral electronics which filter and/or amplify the signals before transmission to the scaling/counting apparatus.

11. A take off device as claimed in claim 10 when in the form of a take off probe for use as a counting device and comprising a carrier receiving slidably take off means which is actuable for reciprocal movement relative to the carrier against a biasing force and operable in conjunction with the light emitter and detector means to generate a signal pulse response on actuation of the take off means against the biasing force.

12. A take off device as claimed in claim 11 in which the take off means comprises a marker device.

13. A take off device as claimed in claim 10 when in the form of a measuring wheel for use in measuring scale lengths in which the wheel has a configuration, such as radial spokes, which makes and breaks light transmission between the light emitter and detector means to generate a signal pulse on rotation of the wheel.

14. A take off device as claimed in any one of claims 10 to 13 in which the integral electronics comprises a filter circuit and an amplifier.

15. Scale rule apparatus constructed and arranged or adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings of Figures 1 to 7.

16. A take off device constructed and arranged or adapted to operate substantially as hereinbefore described with reference to the accompanying drawings of Figures 2 and 3 or 4 and 5 or as modified according to Figure 6.