The temperature of the meter sensor head, hence the temperature readout, must be allowed to stabilise before a comparison reading is taken. In applications where a probe is to be operated in extremes of temperature or over a wide temperature range the temperature dependence of the sensor and electronics must also be taken into account. This system is tried and true but not as accurate as digital and synthetic hair hygrometers. Synthetic hair hygrometers are accurate, but only in a limited range. We do not recommend these as portable units, because the reaction time is slow, and moving rapidly through changing environments will affect the calibration and accuracy of the units.
Problems often occur when using different techniques to compare and calibrate humidity probes.
For example whirling hygrometers often give a higher reading when compared to a fixed probe. Only the thermometers in a whirling hygrometer can be calibrated and errors are often caused in such instruments through poor maintenance, incorrect usage and temperature differences. Errors can easily be introduced when using conversion tables as the relationships between humidity variables are complex. In cases of dispute the calibration of the instruments involved and their traceability should be carefully checked. This depends on the relative humidity, temperature and other environmental factors.