Hi Daniel, > On 5. Mar 2023, at 21:16, Daniel Miazek via subsurface > <subsurface@subsurface-divelog.org> wrote: > > > I've noticed this when I tried to plan a diving on 50 meters and 30minutes > bottom time (including falling down), with 24litres air, 11litres nitrox 52%, > and 6litres oxygen (nitrox 99%). > I used Bulhmann algorithm with 20/80 GF, SAC 19l/17l, PO2 1,4bottom, 1,6 > deco. All ascending speeds 10m/min. > > Generally speaking Subsurface turned out 72 minutes diving plan indicating > that CNS will be 66%, OTU 103. > > I've compared this with my sharewater petrel 3 planner and manual > calculations, and both turned out CNS values close to 49%. > Diving time, gas usage and OTU was almost the same. > > I can share print screens and a file with this particular plan. > Maybe I made saome mistakes in other configuration settings, but I'v checked > everything several times and everything seems to be ok, except CNS > calculations. > > Would be gratefull for any comments or clues. >
what do you use for the last stop depth? If I use 6m 69% whereas I get 47% if 3m is the last stop. If you want more details of what Subsurface is calculating (I might have slightly different settings from you) to compare to your manual calculation, here is the 6m version po2=740 rate=0.000032 for t=299s po2=1268 rate=0.000089 for t=1501s po2=1025 rate=0.000056 for t=154s po2=782 rate=0.000035 for t=86s po2=750 rate=0.000033 for t=20s po2=719 rate=0.000031 for t=100s po2=687 rate=0.000029 for t=20s po2=655 rate=0.000027 for t=1s po2=1568 rate=0.000260 for t=99s po2=1492 rate=0.000137 for t=20s po2=1416 rate=0.000119 for t=100s po2=1340 rate=0.000102 for t=20s po2=1264 rate=0.000088 for t=160s po2=1188 rate=0.000076 for t=20s po2=1113 rate=0.000066 for t=220s po2=1037 rate=0.000057 for t=20s po2=961 rate=0.000049 for t=400s po2=885 rate=0.000042 for t=20s po2=810 rate=0.000037 for t=1s po2=1619 rate=0.000428 for t=339s po2=1467 rate=0.000131 for t=20s po2=1316 rate=0.000098 for t=640s po2=1164 rate=0.000073 for t=20s and here is the 3m version po2=740 rate=0.000032 for t=299s po2=1268 rate=0.000089 for t=1501s po2=1025 rate=0.000056 for t=154s po2=782 rate=0.000035 for t=86s po2=750 rate=0.000033 for t=20s po2=719 rate=0.000031 for t=100s po2=687 rate=0.000029 for t=20s po2=655 rate=0.000027 for t=1s po2=1568 rate=0.000260 for t=99s po2=1492 rate=0.000137 for t=20s po2=1416 rate=0.000119 for t=100s po2=1340 rate=0.000102 for t=20s po2=1264 rate=0.000088 for t=160s po2=1188 rate=0.000076 for t=20s po2=1113 rate=0.000066 for t=220s po2=1037 rate=0.000057 for t=20s po2=961 rate=0.000049 for t=400s po2=885 rate=0.000042 for t=20s po2=810 rate=0.000037 for t=1s po2=1619 rate=0.000428 for t=999s po2=1316 rate=0.000098 for t=40s And here is a write up of how it gets to these numbers: https://thetheoreticaldiver.org/wordpress/index.php/2019/08/15/calculating-oxygen-cns-toxicity/ But I guess the most important part of this is that these are not in any sense high precision numbers but more like ballpark guesses (see the Hamilton quote in the article). Best Robert
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