EFX
Contributor
My Petrel 2 in Rec Mode uses Low, Medium, High GFs of 45/95, 40/85, and 35/75. What is interesting is if I set the computer in Tec Mode, at 35/75, I do NOT get the same NDLs, by 1-2f minutes (more) at 6-=110 ft.
I checked my Perdix when I got home from work and the low, med, and high conservative settings are the same as what you state above. I compared an 80 ft first dive on air for both rec and tec mode using med and 40/85 conservative settings and got 21 and 22 minutes for NDL respectively. Stuartv thought this discrepency could be due to the anticipation of a safety stop in rec mode. I thought the same thing but realized the definition of an NDL is time remaining before a stop is required. A safety stop is just a non-mandatory stop, so a safety stop would be excluded in the calculation.
The difference is probably due to rounding in the calculations. The calculations are done using real numbers but need to be rounded up or down because the NDL display is an integer. This would account for a 1 minute difference but not two. Also, the difference could be due to using different methods to calculate NDL. Rec mode may be using the Haldane equation while tec mode is calculating the deco ceiling using the time remaining to get the ceiling down just past the surface (ceil > 0 ft.) as the NDL. The difference in methods may account for the 2 minutes.
I too am looking forward to an explanation from Shearwater. Anyone from Shearwater care to comment?
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