- -¼ cup water
- -½ cup table salt
- large re-sealable freezer bag
- coffee cup
1) Put ½ cup salt in a coffee cup and add ¼ cup of water. Stir it for a while to saturate the salt (Salt will not dissolve fully in water and it will be like wet sea sand.)
2) Pour this mix in a re-sealable plastic bag and place the Hygrometer in it and seal the bag. (Note: Make sure the mix should not come with the direct contact to the Hygrometer.)
3) Keep this bag in a room having fairly constant temperature for 10 to 12 hours.
4) Check the reading of Hygrometer without taking it off from bag after 10 to 12 hours. The relative humidity in sealed bag filled with mix should be 75%.
5) If the reading is less or higher and if the Hygrometer is adjustable then adjust it accordingly to get 75% reading.
But if the Hygrometer is not adjustable then you have to calculate the temperature manually. For example if the Hygrometer reads temperature of 73% after being in a mix for 10 to 12 hours where in it should be 75%, than you will have to make a note of it and have to add or subtract the difference to your actual readings that is +2% in this case.
Note: It takes about 2 hours to stabilize the Hygrometer before taking accurate reading because of the changes in relative humidity.
