Which is the best type of hygrometer?

With a hygrometer one measures the relative humidity (RH) level inside the humidor. Both digital and analogue hygrometers can achieve a very precise level of accuracy within a specific range. Hygrometers are manufactured taking these particular humidity ranges into account. For cigar storage the base RH level is relatively high: 68 to 75%. Hygrometers produced for standard indoor or outdoor use are not made with the high humidity levels of humidors in mind, this makes a purpose designed hygrometer an essential part of any humidor.

Among the different analogue hygrometers, those which use synthetic hair are the best choice. The humidity level is gauged by measuring the expansion of the synthetic hair. There are less than five manufacturers across the globe who are familiar with the complex production process of these finely-tuned instruments. Almost all other analogue hygrometers measure the humidity level using a metal spiral. This method is very imprecise and can lead to deviations of +/- 5% even with well-calibrated hygrometers. Hygrometers with metal spirals should be replaced as soon as possible with a more precise hygrometer.

Among digital hygrometers, there is a range of products offering different levels of accuracy. Digital hygrometers are in no way fundamentally more accurate than analogue hygrometers. A properly calibrated hair hygrometer is usually significantly more accurate than a cheap digital hygrometer. However, digital hygrometers are less sensitive to vibration and will need to be calibrated less frequently. Most low-cost digital hygrometers are missing a calibration function entirely, which means that, after prolonged use, permanent deviations from the actual RH level are inevitable. When purchasing a hygrometer, you should ensure that the model you choose can be calibrated. The quality of digital hygrometers is based on the coordination between several key components. The moisture sensor plays a major role and the use of inferior quality sensors is often the reason for a limited lifespan, even with otherwise reliable digital hygrometers. Also of note, a costly, precision hygrometer designed for laboratory use will often only guarantee an accuracy of +/- 2%.

When measuring humidity levels, one cannot expect the same accuracy as with temperature measurements.

How do you calibrate a hygrometer?

What kind of liquid should I use to...