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I'd be careful with making assumptions about what other posters know or don't know if I were you. I've done my fair share of instrumental analyses in my time, and calibration and instrument reliability is something I believe I know a little bit about.There we go. Another 'trained' Nitrox user who is unaware that 02 cells degrade over time
As you may - or may not - know, most handheld rec nitrox analyzers have only one user-operable calibration knob. Thus, two-point calibration isn't possible. In an ideal world, two-point calibration would be better, but with those instruments we can't calibrate, only check at two points since there's only one adjustment dial..
Apparently, the analyzer manufacturers have reasons for offering only single-point calibration, and I can offer three probable reasons:
- Two-point calibration (both offset and slope correction) increases the risk that the average user adjusts their instrument way out of calibration. Not good. At all. Particularly given the level of knowledge most people have about calibrating instruments.
- Offset may be more affected by cell age than slope is, so adjusting offset may be good enough unless high accuracy is needed
- If the measured value is fairly close to the calibration value - as it usually is for rec nitrox mixes - a simple offset adjustment is good enough. In rec nitrox diving, you're taught to keep within certain margins, and a slight error in measurement will usually be of no importance.
So, are you saying that rec nitrox divers should start buying pure O2 to properly calibrate their hand-held analyzer? Good luck on implementing that.and need to be checked regurlarly against 2 known mixes, eg air and pure o2
You can't check linearity with a two-point calibration. One point checks offset, two points checks offset and slope, but for checking linearity you need a three-point calibration. IJS.to confirm the cells are still producing a linear voltage change..
It didn't occur to me that you were setting up that strawman, since I thought we were discussing nitrox diving. Well played, sir. Score one.Examples of entry level dive courses include the PADI open water course SSI open water or BSAC ocean diver. Sorry if you do not understand that terminology. I did not say entry level eanx courses.
What about avoiding the gotchas and strawmen now and discussing as adults?