US3058653A - Standard repetitive dive decompression computer - Google Patents

Description

Oct. 16, 1962 M. DES GRANGES 3,058,653

STANDARD REPETITIVE DIVE DECOMPRESSION COMPUTER Filed June 28, 1957 I 6 Sheets-Sheet 1 /ZM pm 1T1: 3. 2 5g. ,Zd

DECOMPRESSION TABLE 0 (m1 of "we 60 ulna) .11

6 b u m if U REPETITIVE GROUP DESIGNATION TABLE INO I nus-urn INVENTOR flat des frazyas BY 6 7 L i ATTORNEYS Oct. 16, 1962 M. DES GRANGES 3,058,653

STANDARD REPETITIVE DIVE DECOMPRESSION COMPUTER Filed June 28, 1957 6 Sheets-Sheet 3 63 sane 7 2319 131.1 LBO It 5'155 "l INVENTOR Alazrza. 0 66' fi/wryes A9. A Qw M ATTORNEYS 1962 M. DES GRANGES 3,058,653

STANDARD REPETITIVE DIVE DECOMPRESSION COMPUTER Filed June 28, 1957 6 Sheets-Sheet 4 INVENTOR ATTORNEYS STANDARD REPETITIVE DIVE DECOMPRESSION COMPUTER Filed June 28, 1957 Oct. 16, 1962 M. DES GRANGES 6 Sheets-Sheet 5 Zone DECOMPRESSION TABLE (an. n: mam. 60 ulna) INVENTOR flair des d/wryes ATTORNEY;

Oct. 16, 1962 M. DES GRANGES 3,058,653

STANDARD REPETITIVE DIVE DECOMPRESSION COMPUTER Filed June 28, 1957 6 Sheets-Sheet 6 STANDARD REPETITIVE DIVE DECOMPRESSION COMPUTER ARBITRARI tau-non TIMES with SURFACE INTERVAL CREDIT TABLE INVENTOR flaziw 0 65 buryes /3. L ATTORNEYS United States Patent Oflice 3,058,653 Patented Oct. 16, 1962 3,958,653 STANDARD REPETETIVE DIVE DECOMPRESSION COMPUTER Maino Des Granges, 3417 Southern Ave. SE., Washington, D.C. Filed June 28, 1957, Ser. No. 668,837 3 Claims. (Cl. 23588) (Granted under Title 35, U.S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to a new repetitive dive decompression computer for embodying the most recent diving data in a new and easily usable form.

The Decompression Problem The blood circulating system of a diver may be said to be, among other things, physically analogous to a charged bottle of soda water. The decompression problem is to get the diver to the surface without allowing any of the seltzer to bubble out of the bottle.

The normal person spends most of his time on the earths surface which may be relatively speaking around sea level; and as a result his blood pressure equilibrates to the air pressure at sea level which is roughly 15 pounds per square inch. This normal blood pressure results from the weight of the earths atmosphere. For every 33 feet a diver descends beneath the surface of the sea, the weight of the water adds another 15 pounds per square inch pressure. At the first 33 feet below sea level a diver is under a pressure which is the equivalent of two atmospheres, or double the normal pressure. This means that the air in the divers lungs is under a pressure of twice atmospheric pressure. As a consequence each breath of the diver has twice as much oxygen as normal and also twice as much nitrogen. The oxygen is burned fairly rapidly and does not cause trouble here, but the nitrogen is the seltzer in the blood. The nitrogen is physiologically inert and does nothing more than go into solution and remain in the tissues. The longer one remains under pressure, the more nitrogen he absorbs until the pressure of the nitrogen in the tissues equilibrates with the pressure of nitrogen in the air being breathed. Equalization however, requires time.

As a general rule of thumb, it is said that the equilibrated pressure of two atmospheres is the maximum from which a diver may ascend directly to the surface without having the nitrogen bubble in his blood and tissues. It takes about twelve hours to so equilibrate, but the deeper one descends, the more rapidly does the tissue nitrogen pressure build up to the maximum two-atmosphere limit. Should an equilibrated diver ascend too rapidly, the pressure of the nitrogen in his blood does not have a chance to equilibrate to the new reduced pressures acting on the diver; i.e. he has not decompressed. As a result he may suffer a sickness more commonly known as the bends in either a mild or violent form, occasionally so violent as to cause death.

Repetitive Diving When a diver surfaces from any dive, he has some excess nitrogen pressure in his blood and tissues. The amount of the excess is a function of the depth of the dive, the time of the dive and the state of his decompression before his dive. When he dives again within 12 hours, he is making his next or a repetitive dive and must now take into account the excess gas remaining in his tissues. Tables were known for determining permissive times of dives that were based on a rule to the effect: Use the combined times on bottom for all exposures and the depth of the latest dive in determining the decompression schedule to use. This rule may be found in the Bureau of Ships Diving Manual, NAVSHIPS 250-880, U.S. Navy Department, Washington 25, DC, July 1, 1952, page 102. Bottom time is here defined as the elapsed time in minutes between leaving the surface in descent and leaving the bottom (deepest depth) in ascent. It is the sum of the time spent in descending and the time actually spent on the bottom. Diving Manual, supra, page 102. Schedule is defined as a particular combination of depth and time during a dive which defines a particular decompression time.

The old rule of decompression procedure failed to give the diver any allowance for the decompression time which he spent on the first dive while coming to the surface, and gave no allowance for the decompression that he actually experienced while on the surface between dives. In addition the old rule was dangerous to a diver when a deep dive was followed by a relatively shallow dive with a short time spent on the surface as will be hereinafter explained.

As described in Research Report 5-57, December 3, 1956, U.S. Navy Experimental Diving Unit, NGF, Washington 25, DO, new Standard Air Decompression Tables have been developed from thousands of dives at the U.S. Navy Experimental Diving Unit. The tables are pri marily for the benefit of the SCUBA (self-contained underwater breathing apparatus) diver or so-called skin divers, and are the best available to date. SCUBA divers generally ascend at a rate of about 60 feet per minute, and the new air decompression table tests were done at this rate.

As described in Research Report 6-57, January 9, 1957, U.S. Navy Experimental Diving Unit, NGF, Washington 25, D.C., new Repetitive Diving Decompression tables were developed. The proposed method is based on the premise that all schedules can be catalogued by their calculated surfacing conditions, and that the cataloguing will allow the equivalent bottom time for a previous schedule to be transferred to a new schedule despite the innumerable combinations that are available.

After close association and observation of innumerable exposures, the decision to limit the instructions for repetitive dives to 190 feet and to emphasize the inherent dangers of excessive depths seems logical and necessary. The Experimental Diving Unit made several deep repetitive dives with no surface interval, with 60 feet per minute rate of ascent and rapid descent. Regardless of the method of computation, the massive changes of pressure appear more than the body desires to accommodate. A diver accomplishing useful work on air at depths greater than 200' feet is tired physically and mentally and not prepared for repetitive dives.

In accordance with the invention, a new method for information concerning safe, repetitive or multiple diving, based on the tables, is advanced; and this invention is directed to a physical arrangement of the tables in a manner whereby safety information for repetitive diving can be quickly and accurately computed and ascertained. The arrangement allows credit for the decompression experienced by the diver in the ascent from the previous dive and the decompression undergone while the diver is on the surface between dives.

In accordance with the invention, a plurality of inter related tables are so arranged on a circular slide rule from which a SCUBA diver can quickly determine decompression times to be used between dives, and ascent times to be used for various depths of repetitive dives.

The slide rule herein disclosed may be called a Repetitive Dive Decompression Computer and embodies the Standard Air Decompression Tables and the Repetitive a Diving Decompression Tables in a new and convenient form for divers and diver tenders.

Another object of this invention is to provide a. simple means for computing the repetitive dive decompression times and to allow the diver quickly and easily to compute with a minimum of error the optimum diving time, depth, and surface interval for the particular situation that he is in.

In a preferred form, the slide rule comprises two outer rectangular scale members that are relatively fixed, but rotatably support therebetween a circular third scale member. Tables are printed on the outsides of the front and back scale members. These front and back scale members are provided with a plurality of openings, properly arranged, from which data can be observed that is printed on the central rotatable scale member in a special way. By suitable correlation of the tables, openings and indicia, a diver can obtain information for safe, repetitive diving.

Other features, objects and advantages of the invention 'will hereinafter become more fully apparent from the following description of the annexed drawings, which illustrate, generally on the same scale, a preferred embodiment, and wherein:

FIG. 1 is a view in front elevation of a preferred computer in accordance with the invention, and shows more partciularly the front scale member and its openings through which indicia on the front face of the circular scale member are visible for a certain adjustment of the circular member;

FIG. 2 is a view in back elevation of the computer and shows more particularly the back scale member and its openings through which indicia on the back face of the circular member are visible;

FIG. 3 is a plan view of the circular scale member disclosing the Decompression Table and Repetitive Group data;

FIG. 4 is a plan view of the reverse side of the circular scale member disclosing the Repetitive Dive Depth and Arbitrary Bottom Times With Surface Interval Credit in dicia;

FIG. 5 is a plan view of the first rectangular scale member marked Decompression Table in a form prior to assembly in a complete computer;

FIG. 6 is a plan view of the second rectangular scale member marked Standard Repetitive Dive Decompression Computer, in a form prior to assembly in a complete computer;

FIG. 7 is a cross-section view of the complete computer in FIG. 1 on the horizontal axis of FIG. 1.

Referring to FIGS. 1, 2 and 7, the Repetitive Dive Decompression Computer comprises front scale member 10, a back scale member 36, and a circular member having a front face or scale 34 and a back face or scale 37. Parts or indicia of scale 34 are visible through openings in front scale member 10; and parts or indicia of scale 37 are visible through openings in back scale member 36.

A central support or grommet 22 is shown at the center of scale 10 for fastening the various parts together and to provide a support for the rotatable circular central member. Other grommets 24, 26, 28 and 30, and 42, 44, 46 and 48 are shown for fastening the first rectangular scale 10' to the second rectangular scale 36 (see FIG. 2) and to allow the circular member to rotate freely therebetween. The two circular scales 34 and 37 may be two sheets glued together, or they may be printed on opposite sides of the same sheet of paper.

The computer is designed to be used for rates of ascent of 60 ft./min.

With reference to FIGS. 1 and 5, the front scale member 10 comprises a rectangular, preferably square, piece of cardboard, wood or'other suitable material of uniform thickness having the printing thereon, except for the reference numerals and their lead lines, shown in the figure. The face of the member 10' can be made of preferably square paper or the like and has openings 12, 14, 16, 18, 20 and 35- arranged as shown. The peripheral arcuate slot or opening 12 on the left side has edges which are marked Depth and Feet. Indicia on circular member 34 are visible through opening 12, the setting being indicative of the depth of a particular dive. The second slot 14 is marked Bottom Time and is radially inward from, but next to, slot 12. Indicia on scale member 34 is set at opening 14 for the bottom time in minutes for the particular diving depth, as later described. The third opening 16 is radially spaced from, but near, slot 14 and is marked Total Ascent Time. Through this slot 16, indicia on scale 34 show the ascent time in minutes. Two lines marked a and b are shown running between slot 14 and opening 16' and are extended across the rectangular scale 10. These lines are used for interpolation when the actual time of a dive does not fit the arbitrary decompression table times of the indicia on scale 34. The fourth opening 18 is located centrally at the top of the rectangular scale 10 and is marked Decompression Stops. A set of numbers marked from 10 feet to 50 feet on the scale 10 at opening 18 are used to indicate the various depths at which a diver should stop for decompression. Indicia visible at opening 18 give the time of the stops at each depth. Diametrically opposite the slots 12 and 16 are respectively similar slots 20 and 35. The opening 20 is marked Repetitive Group, which is explained subsequently.

A table 32 marked Repetitive Group Designation Table for No Decompression Dives is printed on the lower half of scale 10. The lower line of this table represents the depth for dives from 10 to feet, and the repetitive group is indicated on the ordinate or right hand side of the table. Since a repetitive diver has some nitrogen dissolved in his tissue-s as the result of any dive, this table takes that fact into consideration.

The diver may surface immediately from any single first dive listed on the bottom line of the No Decompression table with an ascent rate of 60 feet per minute. For example, at a depth of 60 feet the diver could for the single dive only, without previous dives, ascend rapidly without stops in one minute, provided his bottom time is not greater than 60 minutes. For dives longer in time than those listed in the No Decompression table, the compunter must be used with openings 12, 14 and 18 to find the decompression time.

However, for a successive dive, the diver must find out what repetitive group he is in. For example, should he have gone down to 60 feet for a bottom time of twenty minutes, he would be in repetitive group D. If his bottom time had been 50 minutes he would be in repetitive group H.

FIG. 2 discloses the reverse side of the slide rule, and the second rectangular scale member 36. With reference to FIG. 2, the scale 36 has two slots 38 and 50, and a plurality of openings later described. The slot 38 at the bottom of the scale 36 is marked Repetitive Depth (ft). Indicia on back scale 37 are visible through opening 38 for initially setting the computer at the depth of the proposed succeeding dive in feet.

An indexing bracket with a pointer 39 on scale 36 is shown to set the proper succeeding dive depth on the circular scale 37.

The scale 36 also has printed thereon, immediately above slot 38, a pyramidal table from which a new arbitrary bottom time is determined for a succeeding dive with credit for the surface interval bearing in mind that decompression takes place during surface time. Horizontal openings in scale 36 are provided at each end of each row of this table, starting at the top. The table has letters corresponding to those of the repetitive group of table 32 and the indicia at opening 20 of scale 10. The numbers correspond to the actual time spent by the diver on the surface between dives where the first number is the elapsed time in hours and the second number is the additional time in minutes. Thus at the left hand corner are the FIGURES 2-10 corresponding to a time of 2 hours and minutes. The minimum surface interval has been set at 10 minutes, although the test dives were run with a 6 minute surface interval to provide a small safety margin.

As part of the table a number of letters are shown above each column of the table with the odd letters from A to O on the right hand side of the table and the even letters from B to N on the left. Just below the grommet 22 is the letter Z for the central column. These letters correspond to the repetitive group designation for the previous dive which may be found from the Repetitive Group Designation Table for No Decompression Dives printed on rectangular scale 10 or from the Repetitive Group opening 2%) on scale 10 and the Decompression Table, scale 34.

It is to be noted that normally scale 36 as shown in FIG. 6, when assembled, is rotated 90 with respect to scale It so that slots 38 and 50 overlap slots 35 and 1-2, respectively of scale 10. In use with scale 10 facing the observer, the slots are at the sides, and with scale 36 facing the observer the slots are on top and bottom. In the hands of the operator the rectangular scales 10 and 36 are relatively stationary with reference to the circular scales 34 and 37 which are termed relatively movable thereto. However, it is obvious that either the rectangular or the circular scales may be moved with respect to the operator.

FIG. 3 discloses the information on circular scale 34 and specially arranged for use with the openings of rectangular scale 10, also specially located. Reference may be made to the arrangement of slots and openings on scale 10 for the physical placement of the slots to reveal the data on scale 34. An outside circle of numbers from 40 at the left side of scale 34 reading counterclockwise to 190 refers to a dive depth in feet. A second circle of numbers placed inwardly next to the dive depth corresponds to the depth or bottom time in minutes. These numbers are divided by radial lines and corresponds to times for a particular depth, such as, at 40 feet the times are from 210 minutes to 300 minutes, and at 190 feet the times are from 10 minutes to 60 minutes. This second circle of numbers for depth time is adapted for cooperation with slot 14 marked Bottom Time on rectangular scale 10. The dive depth numerals of the outer circle are used with slot 12 of scale 10.

A third circle of numbers, which read at a right angle to the bottom time circle of numbers, corresponds to the decompression station time and the numbers are marked by brackets with a number corresponding to the depth for which they are used placed in the center of each bracket. These decompression station time numbers are adapted to cooperate with the opening 18 marked Decompression Stops on rectangular scale 10. The right angle placement of the Decompression Stops opening 18 requires the station time numbers to be rotated 90. Thus, a 40 foot, 210 minute dive (FIG. 1 openings 12 and 14) has a stop at 10 feet as indicated in the b column of opening 18 of 2 minutes as shown by the lowest number in the third circle of numbers in the bracket marked 4% at the top of sheet 34.

The fourth circle of numbers, reading from the outside row, are on a line with the bottom time numbers of the second circle, and correspond to the total ascent time. They are adapted to cooperate with the opening 16 marked Total Ascent Time on scale 10. By way of example the radial line below a 40 foot 300 minute dive has been extended to underline a total ascent time of 19 minutes; and a 190 foot60 foot minute dive line extended to show a 183 minute total ascent time.

An inner circle of letters is shown on scale 34 corresponding to the repetitive dive group which cooperate with the opening 20 marked Reptitive Group on scale '10. The diametrically opposite placement of opening 20 with respect to the depth and bottom time openings requires that the repetitive groups be placed away from the depth and bottom time numbers with which they are associated. Thus the repetitive group for a 40 foot- 300 minute dive is group Z under the repetitive group letters in a bracket with the number 40'.

FIG. 4 discloses scale 37 having the new assumed arbitrary bottom time with surface interval credit indicia. The scale has an outside circle of numbers which corresponds to the repetitive dive depth for 40 to feet. An inner circle of numbers corresponds to the arbitrary bottom times for these depths for repetitive group Z. The indicia within the outer circle are positioned radially to cooperate with opening 38 of the second rectangular scale 36 in FIG. 2, and the arbitrary bottom times With the top rectangular opening at the top of the Surface Interval Credit Table printed thereon. By Way of example for a repetitive dive of 40 feet, the time for group Z is on the inner circle of numbers and directly above the 40 foot mark, and is 257 minutes. A line has been drawn to indicate the figures for the other groups. Thus, going to the right of 257 and reading the numbers underneath the radial line, the numbers 241, 187, etc., through 7 are disclosed which correspond to the odd letter group O, M, etc. through A and similarly to the left are numbers 213, 161, etc., through 17 corresponding to the even letters groups N through B. Other data for other depths can be read in a similar manner.

It will be noted from FIG. 4 that the time figures with the exception of the Z group are arranged in radial rows with alternate numbers in each row spaced slightly and arranged at a predetermined angle, shown in the drawings as 90 degrees, to each other. The rows are spaced apart by a submultiple of the predetermined angle so that any group of associated indicia as defined, for example, by the pair of radial lines in the drawing also subtends the same predetermined angle. Since the numbers are arranged alternately in concentric circles, the vertical axes of the numbers appearing in the corresponding openings shown in FIG. 2 as scale 37 is rotated will always appear in parallel planes. Thus the numbers always appear in the same direction and reading the numbers appearing in the openings is facilitated.

Two examples of the operation-of the computer are as follows:

Example A. Assume the diver is making his first dive to 40 feet with a bottom time elapsed to 210 minutes. Referring to FIG. 1, a dive depth of 40 feet and a bottom time of 210 minutes are set by means of slots 12 and 14 with the 210 minute figure on line b. The Total Ascent Time in minutesin opening 16 is indicated to be 3 minutes and the Decompression Station Time indicated at opening 18 above letter b is 2 minutes at 10* feet. The one minute difference in the indicated times is to allow the diver to ascend from 40' feet to 10 feet at the rate of 60 feet per minute and rest at the 10 foot station. Since the diver will take only half a minute to ascend the 30 feet from the 40 foot depth to the 10 foot station, he should spend the additional half minute at the 10* foot station. The tables have been rounded off to the nearest minute for convenience. For this dive the repetitive group at opening 20 is indicated next to the letter b to be group N.

Example B. Assume a first dive of 190 feet having an elapsed bottom time of 60- minutes. The data for a 190 foot, 60 minute dive as shown in FIG. 1 are Total Ascent Time of 183 minutes at opening 16, line a, and repetitive group Z at opening 2 0. The decompression station times of column a at opening 18 are 10 minutes at 50 feet, 17 minutes at 40 feet, 19 minutes at 30 feet, 50' minutes at 20 feet, and 84 minutes at 10 feet which are above letter a at opening 18.

Assume now that the diver of the above examples wants to make another dive, after staying on the surface for a short time.

Example C. Assume that the diver of Example B remained on the surface for 10 minutes, the minimum time any diver should remain. He then wants to make his next dive. He has found that he is in group Z as explained in Example B. The column under Z of the Surface Interval Credit Table on scale 36 lists numbers in hours and minutes. The top number is for surface times up to 22. minutes and gives an arbitrary bottom time of 31 minutes. The next lower number -22 is for surface time from zero hours and 22 minutes to zero hours and 34 minutes, the next lower time, 0-34, is for surface times of zero hours 34 minutes to zero hours and 48 minutes, etc. If a 2 /2 hour surface time has elapsed, the next lower number under the Z column is 2 hours 17 minutes and is used. To get the arbitrary bottom time for 2 hours 17 minutes, the number 15 appears at the horizontal roW in line with 2 hours and 17 minutes, and is that time. The numbers in the opening alongside each row of the table are the arbitrary bottom times for that row of surface times and groups.

To get back to the 190- foot diver with minutes of surface time in group Z, he has a 31 minute arbitrary bottom time for 190 feet. Should he wish to descend again to 190 feet at the expiration of the 10 minute surface time, and gets to his depth and remains there for 20 minutes, then to ascertain his new ascent schedule, he must add his actual bottom time of 20 minutes and the arbitrary bottom time of 31 minutes of group 2 to give 51 minutes as the bottom time to use on the computer in order to allow for dissolved nitrogen still remaining in his blood when he began his second dive. In other words his new ascent schedule will be determined by placing the 190 number at opening 12 and the 60 numeral (which is nearest above 51) at line a of opening 14. This will give an ascent time of 183 with the ascent schedule indicated at column a of opening 18 (FIG. 1).

Example D. Assume that the diver of Example B had remained on the surface for 2 hours and 17 minutes instead of 10 minutes as in Example C. The arbitrary bottom time from the table on scale 36 and opening opposite 2-17 under column Z is minutes. Then the ascent schedule is determined from the sum of this 15 minutes and the minutes of actual bottom time or minutes. The nearest longer time to this on the computer at a depth of 190 is minutes. Adjusting the computer with 190 in opening 12 and 40 in opening 14 the computer will show a total ascent time of 103 minutes, and a schedule of 8 minutes at 40 foot depth, 14 minutes at 30 foot depth, 23 minutes at 20 foot depth, and minutes at 10 foot depth. It will also show that for a third dive, the diver is now in group O as indicated at opening 20.

The old Navy rule would require him to use the minute bottom time from the previous dive on the next dive within 12 hours and would thus bar a repetitive dive within 12 hours. Under the computer he can safely make a repetitive dive as soon as he has had 10 minutes of elapsed surface time.

Example E. Assume that the diver of Example A with a schedule of 40 feet-410 minutes, Group N, wants to make a second dive to 190 feet. With a one hour surface interval, he sets scale 37 at 1 feet with pointer 39, reads down column N on the Surface Interval Credit Table on scale 36 to the next lower time, 54 minutes, and then reads across to the new arbitrary bottom time with surface interval credit of 21 minutes. This new arbitrary bottom time is added to the new actual bottom time to get the total bottom time which is set at slot 14 on scale 10.

Example F. For a repetitive dive to 40 feet with a prior dive of 19 0 feet at 60 minutes, Group Z, the new arbitrary bottom time is 257 minutes for a 10 minute surface interval. The diver may then dive to 40 feet and spend the diiference between 257 and 300 minutes or 43 minutes on the bottom and then use the 40 foot 300 minute schedule and decompression station time.

This last example points up the inadequacy of the old Navy rule since under the old rule he would use the 60 minute previous dive time and if he spent more than 43 minutes at 40 feet after a 10 minute surface interval he would undoubtedly use the wrong decompression schedule and develop decompression sickness.

The Navy rule should be modified since safety demands the use of the combined times and the depth of the deepest dive on repetitive dives. This modification of the old rule requires an increase in the decompression time, a decrease in bottom time and in many cases will bar any repetitive dives within 1-2 hours.

The use of the new decompression tables and the new slide rule should avoid the occurrence of the bends on repetitive diving and allow divers to make repetitive dives within short intervals in safety thereby greatly increasing the speed of salvage operations. The manpower requirements for a particular operation may be reduced by a large amount and more accurate estimates of the number of divers and the time neded for a particular operation may be made.

Even strict compliance with this method will not absolutely insure the diver against decompression sickness. These tables were computed for the average diver. Susceptibility to bends changes from day to day and between divers over such a range that a safe table is prohibitively long. If the diver finds that he is developing unexplained aches and pains when he gets close to the limits of the tables, he should shift to the next lower depth or the next longer time. The tables should be safe for the diver but the diver must make any necessary fine adjustments.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

l. A decompression time computer for divers comprising a support, a movable scale mounted on said support having indicia on a first side corresponding to depth, bottom time, total ascent time, decompression station time, and repetitive dive depth group, and on a second side to repetitive dive depth and arbitrary bottom time with surface interval credit, at first relatively stationary scale mounted on said support for cooperation with said first side of said movable scale having openings for cooperation with said indicia on said first side for calculating the total ascent time, decompression station time, and repetitive dive group from said depth and bottom time, a second relatively stationary scale mounted on said support adjacent said second side of said movable scale and having openings for cooperation with said second side for calculating the arbitrary bottom time with surface interval credit from said repetitive dive depth and said repetitive dive group, a surface interval credit table arranged in vertical columns on said second stationary scale corresponding to repetitive dive groups and in rows corresponding to each equivalent surface interval credit, said openings on said second stationary scale for calculating said arbitrary bottom times with surface interval credit placed in a pattern with each opening placed in a line with one row of said surface interval credit table, and fastening means for fastening said first and second stationary scales to prevent rotation therebetween.

2. A decompression time computer for repetitive diving comprising a support; a circularly movable scale mounted on said support having on a first side an outside circle of numbers from 40 to enumerated every 10 units corresponding to a. dive depth in feet, a second circle of numbers located radially inward from said outside circle on said movable scale corresponding to bottom time during a dive and arranged in a series of groups wherein each group is placed adjacent an associated dive depth, a third circle of numbers located radially inward from said second circle on said movable scale corresponding to total ascent time and having one number for each combination of depth and bottom time, a fourth circle of numbers located on said movable scale having decompression station times from to 50- feet for each combination of depth and bottom times and a fifth inner circle of letters located on said movable scale corresponding to a repetitive dive group associated with each combination of depth and bottom time, the second side of said circularly movable scale having an outside circle of numbers from 40- to 190 enumerated every 10 units corresponding to a repetitive dive depth in feet, and an inner group of numbers located on said second side arranged radially inward from said outside circle corresponding to the arbitrary bottom time for a repetitive dive; a first relatively stationary scale mounted on said support for cooperation with said first side of said movable scale having a first large slot placed at the outer edge of said first stationary scale for setting the dive depth, a second small slot adjacent said first large slot and spaced radially inward from said first slot for setting the bottom time for a particular depth, a third slot spaced radially inward from said second slot for reading the total ascent time for a particular combination of dive depth and bottom time, a fourth slot with indicia from 10 to 50 feet for reading the decompression station time, and a fifth slot for reading the repetitive group letter; a second relatively stationary scale mounted on said support adjacent said second side of said circularly movable scale for cooperation therewith having a first slot placed at the outer edge of said second stationary scale for setting the repetitive dive depth, a surface interval credit table printed radially inward from said first slot on said second scale arranged in columns corresponding to the repetitive dive group and having numbers arranged on a series of rows corresponding to the time actually spent on a surface by a diver, and a plurality of slots arranged radially inward from said outer slot with one slot for each of said rows for reading the new arbitrary bottom time with a surface interval credit for a repetitive dive as set by said first slot on said second stationary scale; and means for fastening said first and second stationary scales together to prevent rotation therebetween.

3. A decompression time computer for divers, comprising a first scale member and a second scale member relatively fixed with respect to each other, and a rotatable member rotatably mounted between said first and second scale members, said rotatable member having a front face facing said first scale member, and a back face facing said second scale member, said front face having thereon a set of circularly arranged indicia dividing the circumference thereof into spaces, each space being indicative of a distinct dive depth and each space having an indicia indicative of such dive depth, said front face having a second set of circularly arranged indicia, said second set being divided into a plurality of groups of indicia, each group being associated with one of said spaces and comprising a plurality of indicia indicative of 10 different bottom times for the dive depth of the associated space, said first scale member having openings Whereby said rotatable member may be set to expose through said openings a predetermined depth dive indicia and a corresponding bottom time therefor, said first scale member covering substantially all of the remaining indicia of said first and second sets; said front face having a third set of indicia corresponding to station stops, the third set being divided into circumferentially arranged groups corresponding to the indicia groups of the second set, the corresponding groups being circumferentially displaced by a predetermined angle, said first scale member having a third opening for exposing the group of said third set corresponding to said associated group, the third opening being circumferentially displaced from said first openings by an amount equal to said predetermined angle, said indicia of said sets being so sloped with respect to each other as to read upstandingly at said openings; said front face having a fourth set of circumferentially arranged indicia indicative of ascent time, said first scale member having an opening for exposing the proper one of said ascent time indicia for the depth and bottom time indicia exposed in the first said openings, said front face also having a fifth set of circumferentially arranged indicia indicative of repetitive dive groups, said first scale member having an opening for exposing the proper one of said repetitive dive group indicia for the depth and bottom time indicia exposed in the first said openings, and a pyramidal table of indicia on the outer side of said first scale member divided into rows and columns, each row and column being marked along one side With an indicia of depth and along the other side with an indicia of repetitive dive group, said back face of said rotatable member having circumferentially arranged spaces marked with indicia representative of depth, and having a plurality of pairs of indicia arranged in a radial group, there being a plurality of such groups, one for each of the last said spaces, the last said indicia being indicative of surface interval credit; said second scale member having a pyramidal table of rows and columns of indicia indicative of bottom times, each row being marked with an indicia of a repetitive dive group, said second scale member having openings along the sides of said table for exposing the proper indicia of said radial groups.

References Cited in the file of this patent UNITED STATES PATENTS 778,790 Merrill Dec. 27, 1904 804,646 Young Nov. 14, 1905 916,563 Kristofek Mar. 30, 1909 1,360,726 Crook Nov. 30, 1920 1,600,591 Johnston Sept. 21, 1926 1,603,847 Harper Oct. 19, 1926 2,674,410 Bernstein Apr. 16, 1954 2,792,993 Schrarnrn May 21, 1957

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