There are two calibration tasks that can straightforwardly be performed by users, as follows:-

Zero-flux baseline calibration. This needs to be performed every time you switch the instrument on, because of the hysteresis property of RH sensor. Baseline settling time depends on what the RH sensor has been exposed to since its last use, but it typically takes 15-30 minutes with an AF200.

Flux density calibration. This needs to be performed at 3-6 month intervals using the the droplet method and the micro-syringe supplied with the instrument. The software handles all the calculations and you're done in less than an half an hour.

In addition, Biox calibrates the RH and temperature sensors built into the measurement heads of new instruments.This is a specialised task that cannot be performed by users. Biox re-calibrates these sensors when instruments are returned for the Passport Service.