The One-Step Calibration Kit utilizes Boveda's 75% relative humidity standard, which is widely used and accepted by chemists and lab professionals to determine the accuracy of any hygrometer (also known as the "salt test"). Hygrometer Calibration Kit is a simple and surefire method to accurately calibrate any digital or analog hygrometer or humidity sensor. Simply place your hygrometer inside the bag, close the zipper, and wait 24 hours. A perfectly-calibrated hygrometer should read 75% RH. If your hygrometer reads above or below that number, adjust the calibration by the number of percentage points it is off from 75%. For even more accuracy, you can buy both RH levels and perform a two-point calibration. Perform the calibration steps in one bag, then move the hygrometer to the other bag and perform another calibration.