How does your Calibration affect the operation... does it...

Say clean Air is 83%...

(a) Change the SIZE of the span (eg 0%O2 is still 30% but 21%O2 is now 83%, so the span is now 53%), or...

(b) Change the REFERENCE of the Span (eg 0%O2 is 33% and 21%O2 is 83%, so you still have 50% total span, but the Reference has moved).

and Finally...

What is the maximum Calibration deviation you are likely to encounter?