Moisture meters measure the moisture content in bulk solids, liquids and gases. Some devices use infrared (IR), radio frequency (RF), or microwave techniques to evaporate water from a sample. Others determine moisture content by measuring a material’s conductance, resistance, or capacitance and calculating a corresponding moisture value. Variables measured include relative humidity, absolute humidity, specific humidity, and dew point. Relative humidity is a measure of the amount of water in the air compared with the amount of water the air can hold at a measured temperature. By contrast, absolute humidity is the mass of water vapor in a given volume of air. Specific humidity is the absolute humidity divided by the total mass of the given volume of air. Dew point is a measure of the temperature to which air needs to be cooled in order for saturation to occur. Moisture meters that measure pressure and temperature are commonly available. These specialized devices often include special circuitry or additional probes.