I am curious how you know that your original hygrometer was reading accurately. Most of the lower price hygrometers are notorious for being inaccurate and can easily be off by 10% or more. The mid range to higher end hygrometers will sometimes be available with a certification of accuracy that shows that the one you purchased has been checked against a NIST traceable hygrometer. It is worth it to purchase one really good traceable hygrometer to use to check all of your other ones against at different humidity points. An easy rough check of a hydrometer can be done as follows:



1.Place some salt in a bottle cap or small cup and dampen it with a few drops of water (without dissolving it). To the consistency of wet sand.



2.Carefully place the wet salt and the hygrometer inside a see-through container and close tightly. You can use a zip lock bag provided it seals good and you leave some air inside as well.



3.Let it sit for 6 to 8 hours at room temperature and note the reading on the hygrometer without opening the container. It should read 75%, the difference is how much your hygrometer is off.



4.If it has an adjustment screw or other adjustment device, adjust to 75% through a small hole made in the bag.





Kelly

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