Keeping your humidor properly maintained is essential. There are several key components, tools, and concepts here, but making sure that your hygrometer is properly calibrated is one of the most essential. Without a working hygrometer, you have no way of knowing for sure that your cigars are protected and at the proper humidity. While calibrating your hygrometer might sound confusing and difficult, it can actually be done very easily with both digital and analog devices. How do you do this? The answer is salt and distilled water.
Calibrating a hygrometer is actually not particularly difficult. You can even calibrate digital hygrometers, even though they cannot be physically adjusted to change the readings. To start the calibration process, you first need some iodized salt, some distilled water and a container to place it in. The container can be almost anything, so long as it has a flat bottom and can hold the salt and water mixture. Once you have found a container, add a flat teaspoon of salt to it. Next, add just enough water to the salt that you form a paste.
Now, you need to measure a level teaspoon of salt and place it in the small container. Add enough water to the salt that it forms a paste. Do not add too much water, as this will skew your readings. You need a paste – do not make it thinner than this. Once you have made the paste, place both the hygrometer (turned on if digital) and the salt solution into the airtight container and close the lid or seal. Leave this alone for about seven hours. Do not disturb the container until at least seven hours has passed.
Leave the container sealed with the salt solution and hygrometer inside for six to eight hours. Once that amount of time has passed, open the container and check the reading on the hygrometer. If it does not read 75%, then the difference between the reading and 75% is how much your device is out of calibration. Ideally, your device should read within between 73% and 77% humidity (+/- 2%).
An analog hygrometer can be adjusted to this range by turning the screw on the back. For a digital hygrometer, you need to write down the amount that it is off and then add or subtract that amount from your regular readings.