Sorry to dig up an old thread, however I had a good friend ask me a question directly related to this discussion. They also dive a shearwater Teric and had left their active gas set to EN32 but were infact diving on air, single AL80. They realised after the dive.
The question is: does anyone know a way to re-calculate the SurfGF from the log file using Air instead of EN32? I imagine if it were possible it would be as simple as replaying the depth and time log through some dive software using 21% O2 - though I don't have any experience with this myself.
Edit: I figured out how to export a log file from Shearwater desktop and simply edit the values of the Fraction O2 column. But there doesn't seem to be a way to import this back into SW Desktop, so presumably need to use other software
Edit 2: I managed to figure out a long winded way. Export from Shearwater desktop as UDDF, Import this into Subsurface. With this method it imports the time and depth logs but with no gas mix. I then manually added the gas mix for air and it calculates the GF based on this.
Playing around with a previously logged dive I'd done on EN32, originally the SurfGF for that dive was 27%. When I ran the Air calculation in Subsurface the SurfGF was 50%. Leaving this info here in case someone finds it useful.