The Xikar is +/- 2% accuracy on RH; the Ambient does not provide this information, but let's say it's the same -- +/- 2%.
That could account for a 4% variance difference right there. The difference between the calibrated and uncalibrated values on the Ambient could be due to the fact that it was calibrated at a higher (75%) RH and you are now at a much lower value.
This is just guessing, and my
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