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If it reads 100% then its fine. Once you can't calibrate it to 100% anymore its failed.
This is fairly normal... you are 5x 21% way up there and tiny mV changes at 21% create much larger swings 79% higher.
Basically when you can't turn up the calibration to meet 100% (as a known gas) the cell is past its useful life for tech diving. It may have a little life left as a recreational 32% cell analyzer but that's when you replace the cell
That's wrong. An new cell is linear from zero to 3.5 bar, an old cell looses linearity. First between 3.0 and 3.5, then between 2 and 3.5 bar and so on. Here we have a cell which is not linear anymore at 1.0 bar and we do not know where the problem startes. Perhaps at 0.95 bar, perhaps at 0.8 bar. Until now no problem with analysing EAN32. But the point of non-linearity will drop down and we do not know when but it will be soon.
You pointed this out yourself... The functional linearity is lost from the top of the curve. So in an analyzer when you're only reaching 98% instead of 100% what does that mean for your accuracy at 32%? Nothing, that is less than 0.5% deviation. You get more variability from barometer pressure changes than this.
