BOVEDA One-Step Calibration Kit - USA
Hygrometers are imprecise instruments that require calibration.
They commonly lose calibration over time and after battery changes.
The 100% sure way of calibrating your Hygrometer is with the Boveda One-Step Calibration Kit.
Each Kit includes a special re-sealable bag and 75% RH Boveda 8grm pouch.
After 24 hours in the bag, you'll know the accuracy of your Hygrometer.
Eack kit will last about a year for multiple calibrations.