How do you calibrate a hygrometer?

[FenDruadin]

I keep reading that you should calibrate your hygrometer before using it in your incubator. So, how do I do that?

Thanks!!

 

[FenDruadin]

Okay, never mind--I just did a google and turned up two different methods that I can try (salt water and wet towel). In case anyone else is wondering:

You can wrap your hygrometer in a wet (not dripping, but not just damp either) towel. In a few minutes, it should read 98% if it is calibrated correctly. If it is not, you can adjust it so that it does (if you have an adjustable type), or you can just record how much it is off by, and use that number to judge the humidity level when using the hygrometer.

Or, you can put the hygrometer in a sealed ziplock bag along with an open container of wet salt (consistency of wet sand, they say). After 6 hours, the humidity should read 75%. Again, adjust accordingly.

Does anyone know why the wet salt thing works? The wet towel makes sense to me, but I don't understand why wet sand would have always exactly the same effect. Anyone?