Quote Originally Posted by deranged chipmunk View Post
There is a free way of calibrating your hygrometers. I do this monthly, only because I need to resupply. If you have a high end cigar shop in your area, they normally have walk in humidors. I have several in my area that do. And these are controlled by state of the art controllers to keep humidity at a constant 70%. I take at least one hygrometer with my when I go to buy cigars and I window shop for a bit while my hygrometers level out. Of course, then I make my purchase and leave. Just take your hygrometers with you, do a little window shopping and split. Free calibrations
Found this: exo-terra thermometer/hygrometer, any good? ... I don't remember my ET digital hygrometer having a calibration option