Boveda 32% Low-RH One-Step Hygrometer Calibration Kit - Standard Small Now you can perform a high and low-RH calibration for your hygrometers. Simply place your hygrometer inside the bag, close the zipper, and wait 24 hours. A perfectly-calibrated hygrometer will read 32% RH. If your hygrometer reads above or below 32%, adjust the calibration by the number of percentage points it is off from 32%. Completely maintenance free - no activation required. Easy to use. Exterior Bag Dimensions: 5.5" x 7" Interior Bag Dimensions: Approx 4" x 4.5" Lasts approximately one year, good for multiple calibrations. Shelf life before opening the pack is a minimum of 2 years.