Expert: Bill Finck Jr. - 1/17/2010

Question
I have a little havanna digital in my box that reads 62% and an oasis electronic humidifer that is set at and is reading 70%. How do I figure out which is correct. and if the little havana is wrong or the oasis is wrong how can i adjust....Joe Z.

Answer
Joe,

There is a method to check the accuracy of a hygrometer - the salt test: Here’s how it works:

Place about 1 teaspoon of salt in a small shallow open container, such as the cap to a jar. Add a few drops of water to the salt. You do not want to dissolve the salt, only get it damp. Place the container with the salt solution in a Tupperware container and put your hygrometer in with it. Put the lid on and allow it to stabilize for about 6 hours. Without opening the container, check your reading. It should read 75%.

Adjusting the hygrometers depends on the model, so you'd have to check your instructions or contact the manufacturer to see if it can be done. The other option is to just note the variance, so you'll know that when your hygrometer reads 70% it is actually 74% or whatever the salt test told you, and just take this variance in to account when checking your humidity.

Hope this helps.
Bill