Analog hygrometers must be calibrated prior to first use. Exceptions to this rule are the adorini hair hygrometers, which are carefully calibrated before shipment. Nevertheless, even the adorini hygrometer may require re-calibration in cases of strong shocks during transport.
As previously mentioned, the accuracy of the prevalent metal spring hygrometers is limited. Higher is the accuracy of the adorini hair hygrometers, which are optimized for the high level of humidity found inside a humidor. Still one should be aware that, in comparison to measuring temperature, measuring humidity is physically less accurate. Even in hygrometers for professional laboratory use at prices of more than $100, manufacturers guarantee an accuracy of only + / – 2%.
Analog hygrometers should be re-calibrated once a year. If a humidor is equipped with a traditional metal spring hygrometer, it is particularly important to pay attention to changes in the humidity level. When using humidifiers based on acryl polymers or sponge-based humidifiers with propylene glycol solution (See explanations about humidifiers) the humidity should automatically stabilize at around 70%. Here one simply needs to refill the distilled water or propylene glycol (for sponge-based humidifiers) as soon as the humidity drops. In the event of doubt, touching the cigars should ascertain whether they are being stored in a suitable climate.