Table correlating device for scuba divers

An apparatus used to correlate and selectively read information from tables dealing with the extent of nitrogen absorption in a scuba diver's body. Tables containing information relating to the amount of time a diver spends at various depths, decompression procedures, the surface interval between repetitive dives, and the resultant amount of nitrogen accumulation in the diver's body are attached to an inner tube. Two side-by-side outer tubes, each having sight windows for selective reading of the tables, are arranged concentrically about the inner tube, and are secured in lateral position by end caps attached to the inner tube. Each outer tube is provided with inwardly projecting flanges on each end which serve as bearing surfaces for rotation about the inner tube. The apparatus is preferably slipped over a scuba tank air hose for carrying.

BACKGROUND OF THE INVENTION 
1. Field: 
The invention is in the field of apparatus used by scuba divers, and 
particularly relates to apparatus used to indicate the extent of gas 
accumulation in the body of a scuba diver. 
2. State of the Art: 
A column of fresh water 33 feet high or sea water 32 feet high exerts one 
atmosphere of pressure. Since the water surface is already at one 
atmosphere pressure, the pressure at a depth of 33 feet in fresh water is 
two atmospheres, and the pressure increases by one atmosphere for every 33 
feet further that one descends. Thus, at a depth of 100 feet, the pressure 
exerted on a diver will be about four atmospheres. 
As a diver descends and the pressure on his body increases, any gases in 
air chambers, such as his lungs, are compressed. At a depth of 33 feet, 
where the pressure is two atmospheres, the volume of air in his lungs is 
compressed to one-half the volume it will fill at sea level. Similarly, at 
100 feet, where the pressure is four atmospheres, the air will be 
compressed to one-fourth of its volume at sea level. 
In order to counteract the effects of pressure on a diver as he descends, 
and allow him to breathe properly, he is supplied with required quantities 
of air from tanks of compressed air. However, even though this permits the 
diver's lungs to maintain their normal volume, and the diver suffers no 
ill effects, the pressure of the air in his lungs is increased in 
proportion to the depth at which he is diving. 
Air is made up primarily of oxygen (about 20%) and nitrogen (about 80%). At 
sea level, approximately one liter of nitrogen is dissolved in an average 
person's body. Nitrogen is about five times more soluble in fat as in 
water so that more than half of the nitrogen is dissolved in body fats, 
even though fats only make up about 15% of the body. 
Due to the increased pressure of air in his lungs, the amount of oxygen and 
nitrogen which dissolves in a diver's body also increases. Nitrogen is not 
metabolized by the body, so it remains dissolved in the body to an extent 
dependent on the external pressure. Oxygen, on the other hand, is 
metabolized and thus is not generally a problem when a diver breathes 
compressed air. For each increase in pressure of one atmosphere, an 
additional liter of nitrogen will dissolve in his body. Thus, at 33 feet a 
diver will have two liters of nitrogen dissolved in his body; at 100 feet 
his body will contain four liters. However, the increased nitrogen does 
not dissolve in a diver's body instantly. Furthermore, the nitrogen 
dissolves at different rates in different parts of the diver's body. Water 
in the diver's body becomes saturated with nitrogen in about one hour, 
whereas fat, which requires much more nitrogen before it is saturated, and 
also has a poor blood supply to carry the nitrogen, reaches saturation 
only after several hours. Thus, several hours are required before the body 
becomes saturated with nitrogen as all of the tissues in the body come 
into equilibrium with the gas pressure in the diver's lungs. 
Unless the diver is at a depth of about 130 feet or more, such that he may 
begin to develop nitrogen narcossis, he will generally suffer no ill 
effects from the increased nitrogen dissolved in his body, as long as he 
remains submerged. However, as he ascends, the pressure on his body 
decreases and excess nitrogen is liberated from his body fluids and 
tissues. If the ascent is too rapid, actual bubbles of nitrogen will form. 
Bubbles forming in the brain, spinal cord, or peripheral nerves can cause 
paralysis or convulsions, or other effects. Bubbles in the joints or 
muscles can cause severe pain. Nitrogen bubbles in the respiratory system 
can cause difficulty in breathing and heavy coughing. In any event, the 
experience is unpleasant and could result in permanent injury. To avoid 
these effects a diver must either ascend slowly enough to allow the excess 
nitrogen to be expelled slowly from his body without bubble formation, or 
he must ascend before too much extra nitrogen has dissolved in his body. 
The amount of nitrogen which actually dissolves in a diver's body is a 
function of the depth to which he descends, and the length of time he 
remains there. 
The U.S. Navy has published numerous tables indicating safe procedures to 
be used to avoid formation of nitrogen bubbles in a diver's body. It has 
been discovered that the mere fact that excess nitrogen is present in a 
diver's body does not mean that nitrogen bubbles will necessarily form. 
Nitrogen can be "supersaturated" in a diver's body so that only an 
insignificant quantity of nitrogen bubbles will form even where the 
quantity of dissolved nitrogen is greater than the amount the body would 
normally hold at a given pressure. The U.S. Navy tables allow some excess 
nitrogen to remain in a diver's body during his ascent. However, it should 
be noted that the various tables are based on an "average" diver. A 
particular diver may be more or less susceptible to formation of nitrogen 
bubbles in his body. 
A diver using the Navy Tables must take into account the fact that when he 
surfaces, his body will be supersaturated with nitrogen to some extent. 
Thus, a diver making a second dive shortly after completing the first must 
adjust for the excess nitrogen in his body. The Navy has published a 
diving manual containing a set of tables for use where a diver makes 
repetitive dives. One of these tables sets forth various times at which a 
diver can remain at specified depths without requiring decompression. When 
a diver intends to make a second or subsequent dive, a second table is 
used to account for the amount of time a diver spends at the surface 
between dives. The second table leads into a third table which tells a 
diver his "residual nitrogen times" at various depths. These residual 
times are the times a diver must assume he already has spent at a given 
depth when he starts a repetitive dive. The U.S. Navy has also published 
various tables to be used where decompression is necessary. Depending upon 
the circumstances, these tables set forth periods of time which a diver 
must spend decompressing at various depths as he ascends from a dive made 
at a deeper depth. 
A diver needs to have access to the information contained in some of these 
tables during each dive he makes. The most common method of carrying this 
information is on a plastic card having the tables printed thereon. 
Typically, a plastic card used for this purpose measures between four to 
six inches wide and between eight to ten inches long, and is provided with 
a hole through which a chain or cord passes for use in securing the card 
to the diver. The problem with use of a card is that it is somewhat 
awkward to carry since it tends to flutter as a diver swims. It is also 
somewhat awkward to use because it is difficult to move from one table to 
another without losing one's place, thus making it likely that one will 
make a mistake and perhaps stay down too long. It is particularly 
difficult for a diver to use when he realizes he has been down too long 
and begins to panic. 
One device that has partially solved these problems is disclosed in U.S. 
Pat. No. 3,058,653. This device is a circular slide-rule type "computer" 
which shows much of the information in windows, excluding much of the 
unwanted information from view. However, the device is designed to be 
carried similarly to the cards, and its size and shape makes it no more 
convenient to carry than a card. Also, the device still uses tables to 
convey some required information, with the attendant risk of slipping a 
line as one reads across, thus reading the wrong information. 
SUMMARY OF THE INVENTION 
The present invention solves the difficulties of using plastic cards having 
diving tables printed thereon, or the device of U.S. Pat. No. 3,058,653, 
by providing tables that may be selectively read and correlated, and are 
carried in a form that is extremely convenient to carry and use. 
This is accomplished by attaching tables containing the desired information 
to an inner tube and arranging one or more outer tubes concentrically 
about the inner tube in a manner whereby the outer tubes are free to 
rotate about the inner tube. Providing sight windows in the outer tube 
allows selective reading of the tables. 
A typical scuba tank is provided with accessory air hoses in addition to 
the air hose used to carry air to the diver. For instance, an air hose is 
usually provided for carrying a pressure gauge so that a diver may monitor 
the amount of air left in his tank. The table correlating device may be 
conveniently slipped over this air hose before connecting said hose to the 
scuba tank, thus holding the device out of the way when unneeded. Yet, the 
diver has easy access to it by pulling the hose around in front of him 
when he wishes to examine the information contained in the various tables.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT 
As can be seen in FIG. 3, the preferred embodiment of the device, shown 
generally at 10, is designed to be attached to an air hose 11 of a scuba 
tank 12. The particular hose 11 to which the device 10 is attached in FIG. 
3, is a hose carrying a pressure gauge 13. This hose is long enough to 
allow the diver to pull the hose around so that he can read the gauge, yet 
the gauge is normally out of the way. Similarly, the device 10 can be read 
when desired, but is generally out of the way. Also, the device fits 
fairly closely around the air hose and does not hang loose, nor does it 
flutter as a diver swims. 
The preferred embodiment of the device includes an inner tube 14 around 
which the other components of the device are arranged. The inside diameter 
of inner tube 14 should be somewhat larger than the diameter of the air 
hose 11. End caps 15, constructed of a flexible material, are friction fit 
onto the ends of inner tube 14. A hole 16 is provided in each end cap 15 
to accommodate hose 11. Hole 16 should have a diameter slightly smaller 
than the diameter of air hose 11 so that the device 10 will be held 
securely in place on the air hose. The material in the area around hole 16 
should be flexible enough to allow the end cap 15 to deform when the 
device is forced past the air hose fittings (not shown) and then spring 
back to its normal shape. 
Various tables of information may be attached to inner tube 14 by means of 
a label 17, or by other method, such as silk screening the tables directly 
onto the inner tube. FIG. 5 shows a typical label which may be used. Shown 
in FIG. 5 as it would appear prior to attachment to the inner tube, label 
17 should be sized so as to cover substantially the entire surface of 
inner tube 14 exposed between end caps 15. Label 17 of the presently 
preferred embodiment of the invention contains four separate tables, three 
of which are particularly designed to be used together. The information 
contained in each of these tables has been published by the U.S. Navy, 
although it has been rearranged here to appear in an original form. The 
first table, designated 18, contains information relative to the amount of 
time spent at various depths where no decompression is required. By 
itself, the value of this table is to set forth the maximum period of time 
a diver may spend at certain depths if he desires to ascend with no 
decompression stops. 
The second table, designated 19, is to be used in conjunction with table 
18. Table 19 accounts for the amount of time a diver remains at the 
surface after one dive before making a subsequent dive. Although table 18 
sets forth safe limits for diving without the need for decompression 
stops, the diver will have some excess nitrogen in his body following a 
dive. As he spends time on the surface following a dive, the amount of 
nitrogen in his body will gradually decrease until it becomes "normal". 
This can require up to 12 hours. If a second dive is made before the 
nitrogen level in the diver's body has returned to normal, the time he may 
spend at a given depth is reduced by a factor proportional to the excess 
nitrogen remaining in his body from the previous dive. Table 19, in 
conjunction with table 20, is designed to take this into account. 
Table 20 is designed to be used together with tables 18 and 19. Table 20 
contains information relating to the amount of excess nitrogen which is 
actually present in a diver's body at some specific period of time 
following a dive, presented in terms of minutes which a diver should 
presume he has already spent at a given depth when he begins a subsequent, 
or repetitive dive to that depth. 
Table 21 is somewhat independent from tables 18, 19, and 20. It is used 
where a diver exceeds the maximum safe limits of table 18 and requires 
decompression stops before ascending to the water surface. However, table 
21 is keyed so that a diver may enter table 19 if he wishes to make a 
subsequent dive. 
Additional information could optionally be added to tables 18-21 concerning 
other depths and bottom times. The information appearing in the tables as 
illustrated in FIG. 5 was selected as being sufficient for the needs of 
most divers and under most conditions. Of course, it would be a simple 
matter to alter the contents of the tables. 
In the past, the information contained in tables 18-21 has been portrayed 
in a manner somewhat similar to that used in the present tables. Although 
a person could work through the tables and find the information he wanted, 
it was not uncommon for the user to inadvertently slip up or down a line 
as he read across. If a diver were to make such an error and failed to 
take into account the full extent of nitrogen accumulation in his body, he 
would run a serious risk of suffering decompression sickness. 
To avoid the chance that a diver might read the table improperly, the 
preferred embodiment of the invention employs two transparent outer tubes 
22 and 23, FIGS. 1 and 2, onto which labels 24 and 25, respectively, are 
attached. As with label 17, use of labels 24 and 25 may be avoided by 
applying the information contained therein directly to the surface of 
tubes 22 and 23, as by silk screening. Optionally, opaque outer tubes may 
be employed and the sight windows actually cut out of said tubes. 
The outer tubes 22 and 23 are provided with flanges 22a and 23a, 
respectively, which serve as bearing surfaces and also serve to space the 
interior surface of tubes 22 and 23 from the outer surface of label 17. 
Having such a space insures that rotation of outer tubes 23 and 24 does 
not wear off the information printed on the label, an especially important 
feature when diving in sandy waters. It is preferable that there be a 
small amount of clearance (not shown) between the flanges and label 17 so 
that rotation is free, and so that water may enter airspace 26 as the 
diver descends. It is also desirable to provide end caps 15 with ports 15a 
to allow free movement of water into the interior of inner tube 14. If the 
device were water tight, there would be a possibility of breakage as a 
diver descended and the water pressure increased. 
Another feature of the invention is the ability to quickly and easily 
disassemble the device for cleaning during a dive if it gets filled with 
sand. This is done by removing one of the end caps 15 from inner tube 14, 
and sliding it away from the device so that outer tubes 22 and 23 may in 
turn be moved away from inner tube 14. Hose 11 passes through each of the 
disassembled pieces so that by shaking of hose 11, water flow serves to 
wash any sand or other material free. The pieces may then be easily 
reassembled. Similarly, it is a simple matter to disassemble the device 
for cleaning at the completion of a dive. 
Outer tube 22 is of a length sufficient to embrace the entirety of tables 
18 and 19 within the flanges. Outer tube 23 is of a length sufficient to 
embrace the entirety of table 20 between its flanges. In the present 
embodiment, table 21 is also positioned between the flanges of tube 22. 
Labels 24 and 25 are illustrated in FIG. 4. Each label is sized so as to 
fit substantially the entire surface of outer tubes 22 and 23, 
respectively. Each of these labels is provided with sight windows which 
permit selective reading of the information contained in the various 
tables. 
Rotation of tube 22 with respect to inner tube 14 permits selective reading 
of the horizontal columns of table 18, and the corresponding Group Letter 
of table 19. The information printed in table 18 represents the number of 
minutes spent at the depth indicated by the corresponding heading printed 
on label 24. Each vertical column of table 18 shows various times spent at 
a given depth. The first column of table 18 represents times spent at a 
depth of 35 feet, the second column represent time spent at 40 feet, and 
so on. Thus, the character "5", designated at 27 would represent five 
minutes spent at a depth of 40 feet. Similarly, the character "25", 
designated at 28, would represent 25 minutes spent at a depth of 100 feet. 
In use, a diver would read from the column corresponding to the deepest 
depth to which he had descended and would rotate outer tube 22 until he 
found the length of time he had spent submerged, known as his "bottom 
time." If his bottom time was somewhere between two of the numbers listed 
in table 18, he would use the larger number. 
A diver wishing to avoid the necessity for decompression would be required 
to ascend before he exceeded the limits set forth in table 18. Thus, a 
diver diving to a depth of 35 feet would be required to limit his dive to 
a total of 310 minutes, 310 being the last number in column 1, the 35 foot 
column. A diver diving to a depth of 100 feet would be required to limit 
his dive to only 25 minutes. A diver exceeding these limitations would be 
required to use table 21 to inform him of the appropriate decompression 
stops that he should make. 
If a diver wishes to make a second dive after completing his first dive, he 
must take into account the excess nitrogen remaining in his body as a 
result of the first dive. The amount of excess nitrogen in his body is 
obtained from table 20. However, this amount is dependent upon the length 
of time he has been at the surface between dives. The surface interval 
between dives is taken into account by table 19. 
To determine the amount of excess nitrogen in the diver's body, tube 22 is 
rotated so as to indicate the length of the dive and the maximum depth to 
which the diver descended, as explained above. The surface interval 
between dives is read in sight windows extending diagonally to the upper 
right from the Group Letter. These surface intervals are expressed as 
hours:minutes. If the actual surface interval is between two intervals 
shown in the sight windows, the next higher interval is used. Thus, if the 
actual surface interval is 3 hours and 35 minutes, and the sight windows 
showed one possible interval of 3:21 and the next higher of 4:19, the 
interval of 4:19 would be used. Although it appears at first glance that a 
diver is getting credit for being at the surface for more time than he 
actually spent, the tables are actually cast so that a diver surfaced from 
between 3 hours 22 minutes and 4 hours 19 minutes only gets credit for 
being on the surface for 3 hours 22 minutes (3:21 plus 0:01). A diver who 
has been out of the water for over twelve hours may assume that all excess 
nitrogen has had time to leave his body. 
After the diver has found the appropriate surface interval, he rotates 
outer tube 23, without rotating tube 22, until sight window 29 of label 25 
lines up horizontally with the selected surface interval. Then he moves to 
table 20. The numbers found in table 20 represent the number of minutes a 
diver must assume he has already spent submerged as he begins a dive to a 
particular depth. 
The following examples will illustrate the manner of use of the device: 
EXAMPLE 1 
A diver enters the water at 8:00 A.M. and descends to 100 feet. He surfaces 
at 8:25 A.M. and wants to know if he can make another dive to 100 feet at 
9:00 A.M., and how long he can stay down if he wants to avoid the need for 
decompression. 
The diver's "bottom time" is "25" minutes in this example. By rotating 
outer tube 22 until the number "25" appears in the sight window under the 
Depth heading "100", and reading to the right, he finds that he is in 
"Group H" at the end of his dive. If he wishes to dive again at 9:00 A.M., 
his surface interval will be 35 minutes. Thus, he will rotate outer tube 
23 until its sight window lines up horizontally with the "0:36" exposed in 
Table 19. After a surface interval of only 35 minutes, the diver finds 
that he still remains in Group "H". Reading the Repetitive Dive Tables 
(table 20), under the heading "100", the diver finds that he must consider 
himself to have already spent 30 minutes at a depth of 100 feet as he 
begins his dive. Thus, he cannot make another dive to 100 feet at 9:00 
A.M. if he wishes to avoid the need for decompression procedures. 
It is interesting to note that the 30 minute figure he obtains from the 
Repetitive Dive Table is greater than the actual time he spent on his 
first dive. However, the information in these tables was published by the 
U.S. Navy, and serves as a standard throughout the diving industry. 
EXAMPLE 2 
Assume the diver of Example 1 decides to dive to only 60 feet on the second 
dive instead of to 100 feet. Looking at the Repetitive Dive Tables under 
the heading "60", he finds that he must consider himself to have spent 52 
minutes at the depth of 60 feet as he starts his second dive at 9:00 A.M. 
Moving back to the Bottom Times table, he can rotate outer tube 22 until a 
blank space appears under the Depth heading "60". Rotating back slightly, 
he finds the number "60" under the heading "60". This means that the 
maximum allowable time he may spend at 60 feet without requiring 
decompression is a total of 60 minutes. Since he already has the 
equivalent amount of nitrogen in his body corresponding to a dive of 52 
minutes at 60 feet, he must limit his second dive to only 8 minutes. 
EXAMPLE 3 
The diver of Example 2 decides to make the dive at 9:00 A.M. to a depth of 
60 feet, but stays down for a total of 25 minutes. Before ascending, he 
checks his time and the tables and finds that he has exceeded the time 
limit for no decompression dives: he has to use a bottom time figure of 77 
minutes (52 minutes from the Repetitive Dive Tables plus 25 minutes actual 
bottom time on this dive). Rotation of outer tube 22 discloses that 
decompression requirements are specified for 70 minutes at 60 feet, and 
for 80 minutes at 60 feet. Using the 80 minute entry, the diver finds that 
he may ascend normally to a depth of 10 feet, at which point he must stop 
for 7 minutes before surfacing. He further finds that he will be in Group 
"L" at the completion of this dive. 
EXAMPLE 4 
After completing the dive in Example 3, the diver wishes to make one final 
dive, this one again to 100 feet. To determine his residual nitrogen 
content, he must rotate outer tube 22 until Group Letter "L" appears in 
the corresponding sight window. 
Before his final dive, he remains surfaced for 5 hours. The surface 
interval sight windows show a next-higher interval of "6:02". Lining up 
the sight window of the Repetitive Dive Tables with the "6:02" in the 
surface interval sight window, the diver finds that he is now in New Group 
"C". Reading the table entry under the heading "100", the diver finds that 
he must consider himself to have spent 10 minutes at a depth of 100 feet 
even as he begins his dive. Rotation of outer tube 22 and reading Bottom 
Time figures for 100 feet discloses a maximum no-decompression dive time 
of 25 minutes. Thus he can make an actual dive of 15 minutes (25 minutes 
minus the 10 minutes from the Repetitive Dive Tables) without requiring 
decompression stops. 
Whereas this invention is here illustrated and described with specific 
reference to an embodiment thereof presently contemplated as the best mode 
of carrying out such invention in actual practice, it is to be understood 
that various changes may be made in adapting the invention to different 
embodiments without departing from the broader inventive concepts 
disclosed herein and comprehended by the claims that follow.