This Technical Report discusses devices in photographic standardization that are used as hygrometers and humidistats in the measurement and control of relative humidity (RH) in test chambers and storage areas. Special attention is given to situations where a photographic standard specifies controlling relative humidity to ± 2 % RH or better.

Electric hygrometers are recommended for their precision, low cost, and accuracy when properly calibrated. Calibration can be done either by the vendor or in-house by a dew-point measurement. Where the budget permits, dew-point combined with ambient temperature measurements (converted to relative humidity) may be the only sensor system.