White Accutemp Hygrometer Is A Household Humidity Indicator Designed To Show Relative Humidity With +/-4% Accuracy On Continuous Basis. Accutemp Is Mfg In A World Class Environment With A Unique Bi-Metal Mechanism Which Works Without Any Batteries. The Gauge Need Calibration Every Year With A Simple Screw Driver. The Product Can Be Wall Mounted On A Screw.