Dr Deco
Contributor
- Messages
- 2,384
- Reaction score
- 96
- # of dives
- I just don't log dives
Dear Texass:
Repetitive Groups
The Repetitive Group was developed by the US Navy table designers to assist divers in a simple method of determining their residual dissolved nitrogen. The ideal system would be to show tables of the inert gas partial pressure in all compartments. Then the diver would select the largest gas load and follow its off gassing till the next dive. [Faster compartments would unload quickly and play no role.] This would require many pages of tables with every halftime for every depth/time combination. Obviously this is too complicated, and the decision was made to simply log the gas loads in the longest tissue and follow the off gassing. Faster compartments would unload quicker than the slowest (obviously). This works wonderfully for deep, decompression diving where the longest compartment is generally the controlling one. In the case of SCUBA, the 120-minute compartment is never controlling since you cannot carry that much gas.
Sixty-minute Control
This prompted Ray Rogers to recalculate the residual gas tables (for PADI) to allow for the 60-minute compartment to control off gassing (for calculation purposes). This is more applicable to the recreational diver.
Deco Meters
A computer actually performs the calculations alluded to in the first section and will find the maximum gas load in the compartments. It will then track the off gassing. In other words, unless you dive a square-wave dive to the maximum limit, and have the 60-minute compartment be the controlling one, the meter and PADI table will not give the same load. The table will indicate a more conservative subsequent dive (unless to the abovementioned limits). Your attempt to track this is an interesting exercise, but will usually give results that are different when comparing the meter and the printed table.
Dr Deco :doctor:
Repetitive Groups
The Repetitive Group was developed by the US Navy table designers to assist divers in a simple method of determining their residual dissolved nitrogen. The ideal system would be to show tables of the inert gas partial pressure in all compartments. Then the diver would select the largest gas load and follow its off gassing till the next dive. [Faster compartments would unload quickly and play no role.] This would require many pages of tables with every halftime for every depth/time combination. Obviously this is too complicated, and the decision was made to simply log the gas loads in the longest tissue and follow the off gassing. Faster compartments would unload quicker than the slowest (obviously). This works wonderfully for deep, decompression diving where the longest compartment is generally the controlling one. In the case of SCUBA, the 120-minute compartment is never controlling since you cannot carry that much gas.
Sixty-minute Control
This prompted Ray Rogers to recalculate the residual gas tables (for PADI) to allow for the 60-minute compartment to control off gassing (for calculation purposes). This is more applicable to the recreational diver.
Deco Meters
A computer actually performs the calculations alluded to in the first section and will find the maximum gas load in the compartments. It will then track the off gassing. In other words, unless you dive a square-wave dive to the maximum limit, and have the 60-minute compartment be the controlling one, the meter and PADI table will not give the same load. The table will indicate a more conservative subsequent dive (unless to the abovementioned limits). Your attempt to track this is an interesting exercise, but will usually give results that are different when comparing the meter and the printed table.
Dr Deco :doctor:
