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21.1 tip

I have an Extech Heavy Duty Dissolved Oxygen Meter (Model 407510). Tech support for this company is terrible, so I'm asking questions here.

The manual says to expect a reading of 20.9 for calibrating to ambient air. I'm getting 21.1. Is this acceptable variation? I am at 2133m/7000 ft ASL.

What is the clear membrane (if that's the right word) end of a DO meter made of? Presumably it is some sort of gas-permeable polymer (?).

Photos here

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    $\begingroup$ That is not an unusual reading for an oxygen monitor at 5500 ft ASL in a well ventilated place. What is the quoted calibration? $\endgroup$
    – Jon Custer
    Jul 18, 2022 at 19:48
  • $\begingroup$ The manual says to expect a reading of 20.9 for calibrating to ambient air. And yes, 0.2 doesn't sound too far off, but then again 19.5, a difference of 1.4, is not considered safe. Just asking. $\endgroup$ Jul 19, 2022 at 10:48
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    $\begingroup$ Listed accuracy is +/-0.7% so seems OK. Are you intending to use that in life safety applications? (“Safe” is a imprecise word, if you don’t understand impacts of oxygen deficient environments please talk to somebody who does.) $\endgroup$
    – Jon Custer
    Jul 19, 2022 at 12:12
  • $\begingroup$ Not an oxygen deficient environment in the sense of someone entering an enclosed space, but thanks for pointing that out. $\endgroup$ Jul 19, 2022 at 17:01

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