I am a retired CIH (Certified Industrial Hygienist). In my last job as a CIH, I was manager of safety and health for a chemical company. We had times when we needed to analyze for chemical contamination (ammonium hydroxide, HCl, and other gases). We had a professional gas analyzer too, with a cylinder of calibrated gas. When we made measurements, we needed to do the calibration before we measured, and after, and record what the readings were on the meter.
I see a pretty cavalier attitude when doing the oxygen analysis, saying that the gas needed to be analyzed before diving. I don’t see much about calibration of these meters. If, as many here state, your life depends upon a very accurate measurement of the amount of oxygen in the tank, then you need to also take calibration seriously too.
I find these technical divers are rather fanatical about testing; I’d like to see them just as fanatical at calibration of their meters, and recording their findings. If you ever need to go to court about an trimix fill, and you have not calibrated your instrument (preferably before and after taking the sample), you may not have much to stand on in a legal case.
SeaRat