A hygrometer is an instrument used to measure the amount of water vapor in the air, on the ground, or in an enclosed space. Moisture meters usually rely on the measurement of other quantities such as temperature, pressure, mass and the mechanical or electrical change of a substance when moisture is absorbed. Through calibration and calculation, these measurement variables lead to moisture measurements. Modern electronics use the condensation temperature (called dew point) or changes in capacitance or resistance to measure humidity differences.