Product review (5 stars): Useful for humidors!
I see from the other reviews that most people use this for HVAC-related uses, but I actually use it to calibrate the hygrometers in my cigar humidors.

As anyone who has every spent time trying to set up a humidor knows, hygrometers are a notoriously inaccurate instrument. Even after calibration, most (maybe even all) humidor hygrometers start to drift one way or another in a very short period of time, and are often off by anywhere from 5-15%, which is a very big deal with cigars, which need 65-70% humidity at all times. Once the humidity drifts over/under that range, you risk getting mold, dry cigars, or even tobacco beetles.

Unfortunately, this meter is too large to leave in either of my humidors permanently, but it is a great way to check on the accuracy of my other hygrometers every once in a while, without having to perform the infamous "salt test". I plan to built a new refrigerated humidor soon, and I will permanently mount this meter in there, rigging up a permanent power supply to the battery terminals. The meter automatically turns off after 30 minutes, but you can bypass the auto-shutoff by holding down the "Hold" button while you press the power button. This will tell it to stay on indefinitely until you press the power button again.

5-stars all the way, for being a meter I can FINALLY rely on for true, accurate humidity readings.