To calibrate a humidity gauge you will need hours, preferably over night.
You would put the gauge in a large zip lock bag next to a small container of salt. Mix a little water into the salt to make it wet.
Zip it and walk away.
After hours the humidity gauge should read 75%.
If it does not then you calculate the difference and that is how much your reading is off.
It it reads only 71% then your gauge is off 4%.
If it reads 50% then your gauge is off 25%.
You would put the gauge in a large zip lock bag next to a small container of salt. Mix a little water into the salt to make it wet.
Zip it and walk away.
After hours the humidity gauge should read 75%.
If it does not then you calculate the difference and that is how much your reading is off.
It it reads only 71% then your gauge is off 4%.
If it reads 50% then your gauge is off 25%.