This Oasis hygrometer, ($27.95 free shipping in North America – ADD $6.00 INTERNATIONAL SHIPPING CHARGE [BELOW] FOR ORDERS OUTSIDE THE US/CANADA) works great! I attached mine to the hatch of the storage compartment in my guitar case. I keep it set off to one side so the neck of the guitar clears it. The Oasis hygrometer oasis, ($27.95 free shipping in North America – ADD $6.00 INTERNATIONAL SHIPPING CHARGE [BELOW] FOR ORDERS OUTSIDE THE US/CANADA) main draw back is that it stays on. You need to turn it off to save the battery. The Oasis hygrometers oasis, ($27.95 free shipping in North America – ADD $6.00 INTERNATIONAL SHIPPING CHARGE [BELOW] FOR ORDERS OUTSIDE THE US/CANADA) in North America) gives you instant measurements of temperature and humidity. A guitar, or any other stringed musical instrument made of wood, is at risk of cracking when the relative humidity drops below 40%. The Oasis® Digital Hygrometer ($27.95 free shipping in North America – ADD $6.00 INTERNATIONAL SHIPPING CHARGE [BELOW] FOR ORDERS OUTSIDE THE US/CANADA), accurately measures relative humidity and can help you decide when to use your Oasis® Guitar Humidifier. With our new convenient case clip, it is now possible to measure the relative humidity inside your guitar case with the Oasis® Digital Hydrometer ($27.95 free shipping in North America – ADD $6.00 INTERNATIONAL SHIPPING CHARGE [BELOW] FOR ORDERS OUTSIDE THE US/CANADA). This unit works great for helping to humidify violin family, humidify mandolins, humidify dulcimers, humidify mandolins and any other wooden, stringed instrument. Oasis® Digital Hygrometer/Thermometer ($27.95 free shipping in North America – ADD $6.00 INTERNATIONAL SHIPPING CHARGE [BELOW] FOR ORDERS OUTSIDE THE US/CANADA). (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 Oasis Digital Hygrometer/Thermometer OH-2$27.95 International Shipping Charge $6.00 Black Cat Fingernail Sandpaper $3.95 Oasis Guitar Humidifier $16.95 Oasis OH11 clip on tuner $16.95