Product review (1 stars): Accuracy range (humidity) is too wide for any meaningful use on the units I got  -  YMMV
Badly out of calibration.  Ordered one from Amazon, and it was at the lower end of the calibration range part of the time (read 70% in a regulated 75% RH environment), rest of the time was out of the the range (read <70% RH).  Amazon replaced it without question, but the new unit was even farther outside the range.

These little units are NOT configured so you can adjust the displayed RH as some other units are.

If you need to know what the relative RH is with any degree of precision, these are not the units for you.  Extech seems to think +/- 5% is good enough.  If they made clocks with that level of precision, you could get a clock that could gain or lose one hour and 12 minutes every day and it would be considered accurate..

If you want to maintain your humidor between 65-70% RH.  When it is really 60-65% there will likely be an unpleasant surprise.

And yes, I could just mentally add 5 or 6 or 7 or% to the readout, but that's not why I paid my money.

Avoid this unit if precision is important to you .