How do you know when to use your Oasis humidifier? A digital hygrometer clearly indicates when to use the humidifier. A guitar, or any other stringed musical instrument made of wood, is in risk of cracking when the relative humidity drops below 40-45% in the room where it is kept. Keep in mind that weather reports are not a good indicator, since indoor humidity may vary considerably with outdoor humidity. You can remove any doubt with a simple digital hygrometer. Digital hygrometers are best because they are more accurate and don’t need to be re-calibrated. There are no springs or moving parts to wear out. We think that a good hygrometer is so important to the protection of your musical instrument that we had one produced to our own specifications! Oasis Digital Hygrometer/Thermometer (3.0 v 2032 battery included – annual replacement needed) Guaranteed for 5 full years Super-slim profile design with secure Velcro mount fits anywhere Advanced humidity sensor maintains exceptional accuracy for years Records high/low temperatures Measures temperature in C or F On/off switch Measures: 4″ x 1.25″ x .375″ Humidity Measuring Range…………20% to 90% RH (Relative Humidity) Resolution…………………….. 1% Updating time……………….10 seconds.