The oceanic data format has a header and trailer block before and after the sample data. The starting and ending tank pressure is stored there. I should have more detailed info somewhere in my notes.
I couldn't find it in the header. But the way they seem to steal bits from here and bits from there to patch information together I could look a long time and still not find it. I will try looking at the trailer too. If you could find it in your notes that would be super too. ;)
The goal is to have the data format nicely documented, but I just didn't have time for that so far :-(
Documentation always seems to be the lowest priority. I understand completely.