Calibration standards for the most accurate measurement include the gravimetric hygrometer, chilled mirror hygrometer, and electrolytic hygrometer. The gravimetric method, while the most accurate, is very cumbersome. For fast and very accurate measurement the chilled mirror method is effective.[18] For process on-line measurements, the most commonly used sensors nowadays are based on capacitance measurements to measure relative humidity,[19] frequently with internal conversions to display absolute humidity as well.