Hi CaptBones,
thanks for sharing your experience. Very informative
Indeed, the VIIC manual mentions the Orsat device. My guess is that the crew did not measure the O2 content during all dives, but relied in most cases on experience and just estimates based on elapsed time. In particular, because (as you mention) a lower level would not be immediately lethal.
If you had the choice would you prefer a CO2 model or an O2 model? Or are you just not happy with the messages?
Regards, LGN1