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Understanding How a Hygrometer Measures Relative Humidity

Hygrometers measure relative humidity, meaning the amount of water vapor in the air and a small, enclosed space. For the sake of your cigars, the small enclosed space just happens to be your humidor. The humidity level inside your humidor can greatly affect the condition of your cigars, and ultimately their taste when being smoked. Cigars that have too low humidity will have reduced (or even no) taste to them. Without taste, you may as well be smoking cigarettes. On the other hand, cigars that are too humid can prove difficult to light since they are too moist. In extreme cases, overly humid cigars can start to develop mold inside.

The term "relative humidity" is often indicated on a hygrometer with the initials RH. The readout on a micrometer is a percentage, indicating how saturated the air is with water vapor. Seeing a readout that lists "% RH" is common for relative humidity. If the relative humidity reads at 50% RH then the air is 50% saturated with water vapor.

Relative humidity can be greatly affected by the temperature of the air. If water vapor is not added to the air, and increase in temperature can cause a decrease in relative humidity. If your humidor is moved to a room that has a drastic change in temperature, you will likely see a change in relative humidity on your hygrometer reading.

Since relative humidity is such an incredibly important factor in maintaining your cigars, a hygrometer should be an essential part of any humidor. Many (though not all) humidors include an analog hygrometer on the front face.

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The first analog hygrometers relied on horse hair to measure relative humidity. Horse hair would be wound around the wound springs and other mechanics inside the hygrometer gauge. As humidity would arise, the horse hair would expand and move the springs inside, which would move the needle on the gauge to indicate a raise in the relative humidity level. The needle would move in the opposite direction as the horse hair would contract if there was a drop in relative humidity. Some analog hygrometers are still made this way today, and many antique hygrometers will rely on this technology, however most modern analog hygrometers rely on metal springs to provide a reading on the gauge. Some hygrometers use psychrometers (or wet and dry bulb thermometers) to determine the changes in relative humidity.

Ideal relative humidity ranges for most cigars will be between 65% and 70%. As you explore your cigars, you may find that you prefer different brands of cigars at different humidity levels. That is totally fine! Find the levels that work best for you without damaging your cigars, but 65-70% RH is a great range to start off at.

It is important to remember that a hygrometer does not measure the humidity inside each individual cigar, but rather the air in the humidor surrounding your cigars. If you have recently purchased cigars, it is very likely that there humidity is not the same as what is being read on your hygrometer. It usually takes a day or two for the humidity levels of brand new cigars to adjust.