All hygrometers are not created equal as I have found out. 1 went in the trash today, it was a CI freebee (the blue ones) that was not adjustable and totally way off. My other 2 are going through a salt test now a Little Havana and a Hygroset. Honestly, so far the Little Havana is the closest to being true. The Hygroset I have salt tested before and adjusted, BUT when it goes in the humi it reads high. I have a Xikar rectangular hygrometer on the way, should be here tomorrow.
With that said, I really only use the hygrometer to show me when the RH drops so I can give the Heartfeelt beads a spray. The key to my success in the humidor has been the beads. In reality I could throw out the hygrometers and still have perfect conditions for my cigars