I have 2 acurite Hygrometers, I did the salt test and checked them this morning. One was 12 off the other 14, I can't find my instructions and don't see any obvious way to calibrate them manually. Any help, please!
Some hygrometers have a screw on the back that you can adjust.
However most of the time you are not going to actually be able to *calibrate* it as such, in the sense of adjusting the dial... what you need to do is put a piece of masking tape somewhere on the front that says "subtract 12 for real #" (or whatever the relationship is for your particular hygrometer). And then, when you read it, make the adjustment mentally -- so if it is reading 12 points high, and you are aiming for an actual humidity of 40%, you want the dial to read 52%.