Choose an indicator for %RH measurement only, %RH and °>F measurements, or %RH, °>F and °>C measurements. All models have a cellulose RH sensor that measures relative humidity from 0 to 100% RH. Thermohygrometers feature a bimetallic temperature sensor.
Models 03310-20 and 03310-40 include a test certificate ensuring conformance to stated specifications. All indicators have a solid brass case, a 5" diameter glass face, and predrilled holes for wall mounting.