Calibration of hygrometers
Hygrometers can suffer from bias and long-term drift. Therefore calibration is essential for accurate humidity measurement.
For a hygrometer, this comparison might be against a calibrated reference hygrometer at a calibration laboratory. The reference hygrometer should itself have measurement traceability directly, or in multiple steps, back to an authoritative standard.
For some hygrometers there are also methods of "field calibration" - for example using salt solutions to generate values of relative humidity - which can be made traceable.
5 of 12