Another way to test the calibration of your hygrometer is the salt method. Here's how to test your hygrometer using the salt method:
- Place a teaspoon of salt in a bottle cap or small cup and dampen it with a few drops of water (without dissolving it).
- Carefully place the wet salt and the hygrometer inside a see-through container and close tightly. You can use a zip lock bag provided it seals well and you leave some air inside as well.
- Let it sit for at least 6 hours and note the reading on the hygrometer without opening the container. The hygrometer should should read 75%. The difference is how much your hygrometer is off. For example, if your hygrometer reads 70% during the salt method test this means that to obtain the real humidity level you should add 5 points.
- If you have an analog hygrometer, you can correct the reading. You will need to adjust the needle to the 75% mark by turning the screw on the back using a small screwdriver. Your hygrometer is now ready to be placed inside your humidor.