Dive planner CNS calculations

Willem Ferguson willemferguson at zoology.up.ac.za
Fri Nov 9 00:19:38 PST 2018


Hi Robert,

I have been doing some testing, as you have seen from emails on the mail 
list and have looked at the existing Subsurface code in divelist.c.

With respect to the calculation of CNS%, your and my calculations are 
identical EXCEPT that, for a specific PO2, you only use the next-lower 
tabulated maximum time and do not interpolate to provide for a PO2 value 
that is intermediate between two tabulated max-time values (line 214 in 
divelist.c). We use the same table originating from the NOAA Diving 
Manual and I think that is safe. Therefore the Subsurface CNS% values 
are slightly conservative.

With respect to the calculation of OTUs, you use an analogous but 
different formula from the one provided in the Baker document. At this 
stage I would not say that the formula in the existing code (line 165 in 
divelist.c) is better or worse than that of the Baker document (taking 
into account other bugs in the Baker document). But do you have any idea 
where the formula in divelist.c comes from? I would like to do more 
reading around the issue to come to a sensible conclusion about these 
differences.

Kind regards,

willem





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