Things you need

1. Small plastic bottle cap

2. Regular table salt

3. Water

4. Small zip lock bag

Calibrating your hygrometer

1. Fill the bottle cap or small cup with salt and dampen it with a few drops of water (without dissolving it).

2. Carefully place the wet salt and the hygrometer inside a see-through zip lock bag and close tightly, leave some air inside as well.

3. Let it sit for at least 6 hours and note the reading on the hygrometer without opening the container. The small cap of moist salt should humidify the bag to 75% as your hygrometer should read.

4. If it does not read 75% you can adjust the needle to 75% by turning the screw on the back.

5. If you use a digital hygrometer you simply need to use the + and - button to increase or decrease the percentage of humidity.