| Absolute humidity | Indicates the amount of water contained in 1m³ of air. |
| Humidity hose | Fabric hose which is drawn over the thermometer of a Psychrometer. The hose is moistened and is used to measure the wet bulb temperature |
| Wet bulb temperature (humidity temperature) | Wet bulb temperature, measured at the moisturized thermometer of a Psychrometer. The wet bulb temperature results from the chilling because of the evaporation at the moisturized thermometer. |
| Hygro-transmitter | General term for humidity measuring instruments with an electrical measuring value output. |
| Hygrograph | Mechanical measuring instrument for time-dependent recording the relative air humidity. |
| Hygrometer | General term for indicating humidity measuring instruments. |
| Hygrostat | Humidity-dependent switching instrument to control moistening or dehydrating devices or to trigger warning signals indicating too little or too much moisture in moisture-sensitive-installations. |
| Capacitive Measurement element | An arrangement in which a change in the relative humidity leads to a change in the electrical capacity. For example, the capacity of a polymer film on a carrier material changes when water vapour is absorbed. |
| Measurement element H | Specially prepared human hairs expand under the influence of humidity, thus changing in length. This change in length is a measure of relative humidity. The range of application lies between 10 and 100 % rel. humidity in temperatures ranging from – 60 to + 70 °C. Hair measurement elements must be regenerated. |
| Measurement element K | Under the influence of humidity, specially prepared synthetic fibres change in length. This change in length is a measure of relative humidity. The range of application lies between 0 and 100 % rel. humidity in temperatures ranging from 0 to + 100 °C. |
| Psychrometer | Measuring instrument for determining the air humidity by measuring the dry- and humidity temperature and by means of a Psychrometer formula. Thanks to its good measurement accuracy attainable the instrument is used also as reference device. |
| PT 100 Resistance Thermometer | The temperature-dependent change in resistance of a measurement coil made of platinum wire is used as a measure of temperature. 100 for 0°C is usually used as the basic value (Pt 100). The time-dependent resistance values are standardize in IEC 751. It is applied in psychro-transmitters. |
| Relative humidity | The percentage ratio of the absolute humidity to the saturation amount of water in the air at the current temperature. |
| Dew point | A measure of the absolute humidity in the air. States the temperature where the saturation point is reached under cooling. |
| Tensiometer | Measuring instrument for measurement of the saturation potential of the soil (water requirements of soils). Important to determine irrigation requirements. |
| Dry temperature | The ambient temperature measured on the dry ventilated thermometer of a psychrometer |
