How to calculate/extract Tank "Guage Presure" form T1 sensor

Hi All,

 

I have a use case where I am trying to calculate the Tank pressure from the resulting FIT file that is produced from my MK2i combo.

T1 is connected to Tank, pressure reads perfectly on Watch, the resulting FIT file when uploaded to Garmin Connect looks good giving the correct Tank pressure at various time points.

Using the SDK, I use the same FIT file to read the Tank pressure, I believe this should be contained in the RecordMesg class/object (depending on the language you are using).

In the record Message I can get the Timestamp, Depth, NDL time (seconds) and absolute pressure(Pa). 

The hope was that the Gauge pressure could be ascertained from the Absolute pressure, depth and lets say one additional atmosphere for the above water pressure. However, the maths do not seem to work out on this.

i.e.   At a depth of 24.212m I have an absolute pressure of 345646 Pa, even before taking away any additional pressure to find the gauge pressure, this number in Pa directly to Bar is 3.45646 bar. I would certainly hope that at 24 meters I was never near 3.4 bar in a single tank setup lol.

This would lead me to believe that my ATA is calculated from the absolute pressure reading i.e.

345646 Pa -> 3.45646 bar -> 3.41125987258 ATA Which seems to be about what I would expect at a depth of 24 meters.

 

So if Absolute Pressure is for ATA, can I get the Tank Pressure from the same FIT file?

Anybody ever done this or can give guidance on how to get Tank Pressure at different points from the Dive?