A hygrometer measures the humidity and water vapour in the air. A thermohygrometer measures both humidity and temperature.
Within a volume of air, the maximum amount of water vapour it can hold varies greatly by temperature with cold air holding a fraction of what warmer air will. Most moisture meters use temperature to give the relative humidity (RH) for a particular temperature and display it as a percentage. Most models have a built-in digital LCD display but there are several which use an analogue readout, these are primarily for continuous monitoring.
These instruments all feature built-in displays and some offer features such as datalogging, web bulb temperature or dewpoint.
RS offers a range of thermo-hygrometers, many of which can be calibrated to UCAS or RS Calibration standards to ensure accurate measurements.
Primarily, thermo-hygrometers are used to test HVAC systems and office environments. They often feature a probe which can be inserted through an air-conditioning duct to get readings from within the ducting.
A hygrometer measures the moister in the air and a moisture meter measures the moisture within a material such as wood, paper or stud walls.