A hygrometer is the instrument that measures humidity.The two main types of hygrometers are analog and digital. While methods for calibrating/adjusting hygrometers varies between products, the following methods will help you establish an accurate benchmark.
Checking Hygrometer Accuracy:
Table Salt Method
Mix 1/2 cup table salt and 1/4 cup water in a vessel, then place in an airtight container (i.e., ziptop bag). After 24 hours, at room temperature, the humidity in the bag will be 75% (RH) - table salt will seek equilibrium at 75 RH. Adjust your hygrometer accordingly, or just remember what +/- to factor in.
Damp Towel Method (less accurate)
Wrap your hygrometer in a damp (but not dripping) towel for 20 minutes. Afterwards, the humidity in the towel will be 98% (RH).
TOUCH & FEEL
While it is helpful to use a hygrometer when quickly checking the condition of your cigars, there is no substitute for your sense of touch.Every connoisseur knows that cigars must be felt to ascertain their condition and disposition.A cigar should feel silky and smooth to the touch.A well conditioned cigar should yield slightly when gently squeezed between your fingers.The wrapper should not crack or make a sound.When you release the depression, the cigar should slowly regain its shape.