A dependable way to make certain your hygrometer is accurate and your humidor functioning is the Calibration Kit from Humidipak. This is a new entry on the market from the same company that brings you the Humidipak humidor bags for the temporary storage of cigars.
The Calibration Kit consists of three bags. Each is engineered to produce and maintain a particular humidity level. The first bag is set to 32 percent, the second to 52.5 percent, and the third to 75.5 percent relative humidity. The bags are guaranteed to maintain that level of humidity for 12 months.
Just tear off the top of the plastic bag and insert your hygrometer, then completely seal the Ziploc top. Leave the hygrometer in the bag for 24 to 36 hours as advised. Start with the lowest humidity level bag, 32 percent, and work your way up. When finished, you should have an accurate calibration of your hygrometer's conditions. The bag readings have a variable of plus or minus 0.3 percent.
The Calibration Kit retails for $49 and is available by calling Humidipak's toll free number, 1-877-892-1720.