1) Table Salt
2) Water Bottle Cap
3) Plastic Zip Lock or Air Tight Container
Fill the water bottle cap with about a tablespoon of salt.
Dampen the salt with water, should be 10-15 drops. Do not dissolve the salt.
Place the salt cap and the hygrometer in your bag or container for 12 hours.
After 12 hours your hygrometer should read 75%.
If it does not and your hygrometer can be adjusted proceed with correcting it.
If your hygrometer does not allow for adjustment remember how much it is off by and make a mental note for the future.
ie. If your hygrometer reads 71% after completing the calibration (and can not be adjusted) 68% would be the equivalent of 72% within your humidor. Same can be said if it reads 79% after calibration 76% would be the equivalency of 72%.