Xikar is the only manufacturer of hygrometers that I use. They are calibrated from the factory but I always salt test them and re calibrate every 6 months or so. Most of the time they don't need it. I have found that if you let the battery run low it will begin to read incorrectly. Change the battery every 6 months when you check the calibration and all will be fine. I also use the rectangle one in my other humidors and I like them both. This one fits in the stock round notch for the analog hygrometer so I use this one for my 50ct humidors and the rectangle one of all the other lager ones.
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