Never have to wonder if your digital hygrometer is accurate again. The HygroSet III FM is designed as a replacement for many front mount analog hygrometers. The HygroSet digital hygrometers are the first digital hygrometers of their kind – capable of being adjusted after calibration. Each click of the adjustment knob changes the humidity display (+ / -) by 1%. Used in conjunction with Humidipak’s (Boveda) One-Step Calibration Kit (sold separately), you are able to perform the 75% salt test on your new hygrometer. Simply place your HygroSet or HygroSet II in a Ziploc bag along with the Humidipak and seal the bag. After 24 hours, increase or decrease the humidity output control to 75% to ensure that your hygrometer is perfectly calibrated. This process and the HygroSet Digital Hygrometers make sure that you do not have to memorize or label the differential for your hygrometer. The HygroSet Series measures both humidity (accuracy +/- 2% from 20% to 90%) and temperature (accuracy +/- 1 degree – displayed in Celsius or Fahrenheit). The HygroSet II is round with a 1 7/8” Diameter and a ½” thickness.