Product review (3 stars): No Calibration
I just bought it yesterday from Guitar Center. I bought it because they only sold this one, so I gave it a try. So far it function as it suppose to. I used it against a cheap analog hygrometer and I assume that it reads a lot more accurate than the analog one. The downside is that it cannot be calibrate. I could not find anywhere in the manual that says it can (I asked the guys in GC, and they had no idea what I was talking about). So you will need a lot of faith to believe that it is accurate enough, unless you have another one (or 2) to compare against it. And I hate to spend another 20 bucks for another hygrometer just to compare with it.

Overall, this hygrometer works fine. It looks sharp and fits perfectly in my guitar case. I'll have to see more in the future if there will be any issue with it. No calibration, so you can't do any salt test. Next time if I buy another hygrometer, I'll definitely choose the one that can be calibrated.