Re: Decompression Calculations
Date: April 30, 2019 07:14PM
There are two factors the OSTC always figures in, whereas in Multideco you have to explicitly set them:
1) Residual saturation from previous dive(s) - propably not the dominating factor in your case.
2) Surface pressure. Default in Multideco is to calculate for sea level. The OSTC takes the ambient pressure that is shown in the surface mode screen. What pressure do you have / had when yielding the above results? When i set my Multideco to 750 m height, it calculates an even longer TTS than your OSTC did, so i assume you may be sitting somewhere at 500 m above sea level and/or in an area with low(er) air pressure due to weather.
As air is a pretty ineffective deco gas and 6 meters is quite deep for final decompression on air (so ineffective in it's own, too), these two factors amplify the effect of the surface pressure on the duration of the last stop.
Last but not least, the OSTC puts in a final ascent from the last stop to the surface with 1 meter / minute. So a last stop at 6 m will add 6 minutes to the TTS. This is done because the diver should do it because it's healthy to do and also to incorporate a little safety margin in the gas needs calculation.