One could also calculate each SAC rate individually and then average those averages but this would mean that the overall SAC rate could not be calculated unless you had the complete information for each tank individually. That is we add up all the gas use and apply that to the dives overall duration and overall average depth. What we do is calculate the overall average for the dive. There is really no formal definition in diving terms (remember that SAC rate was originally used to calculate the likely air consumption when planning a dive in the days when SPG's (submersible pressure gauges) were not yet available). We try to err on the side of caution, so if we do not have sufficient information to calculate a specific SAC rate or if there is conflicting information (for example a tank is specified and has gas used but does not show up in the profile then it is likely that the SAC rate would be inaccurate as there is no way to account for this "extra" tank).įinally, the "overall SAC rate" is subject to a bit of definition. Things are a bit more complicated in the case of CCR rebreathers as the dive computer typically only tracks the Diluent as a gas so we use some heuristics to assign the Oxygen tank's use to the appropriate section of the dive. As you note, the Perdix will provide that gas switch information so as long as you have filled in all the tank information for each tank used on the dive you should see a SAC rate for each tank as well as the overall SAC rate. In order to get the average depth and duration we typically need to have a dive profile downloaded from a dive computer (in the case of dives without a profile it is possible to manually enter the average depth and dive time and we can then calculate the overall SAC rate) that contains gas switches. a Start Pressure, End Pressure, Tank Size and, in the case of US/Imperial calculations, the Tank Working Pressure) as well as the average depth during the period of the dive in question as well as the duration of that portion of the dive. In order to calculate the SAC rate, you need the amount of gas used (i.e. If that information is not available, the the SAC rate for that portion of the dive or the overall Sac rate will not be calculated. In order to calculate these SAC rates we do need to have enough information to do it. the SAC rate during the portion of the dive that that gas was used) as well as an "overall SAC rate". Dive Log DT and Dive Log Manager (as well as Dive Log on iOS) calculate the SAC rate for each gas individually (i.e.
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