Take the guesswork out of protecting your instrument. When the relative humidity drops below 40%, a guitar, or any wooden musical instrument, is at risk of cracking or warping. The Oasis OH-2C Digital Hygrometer accurately measures relative humidity, helping you decide when to protect your instrument with the Oasis Guitar Humidifier. The OH-2C is identical to the OH-2, except that it allows for humidity calibration. Calibration allows the user to adjust the hygrometer +/- 5 RH points if any changes are needed.