What is the hygrometer ‘salt test’ and how do I do it?
As with any measuring instrument, hygrometers are only useful if they have been properly calibrated before use. The salt test is an excellent, cheap way to test your hygrometer’s accuracy.
Be sure to have the following items on hand:
1. Fill the bottle cap about ¾ full with the table salt.
2. Slowly add the distilled water to the salt, mixing with the small stirrer, just until the salt becomes a very thick slurry. DO NOT add too much water, because this will throw off the results of the test.
3. Put one of the bags inside the other, so you will be able to create a double seal.
4. Place the bottle cap and the hygrometer inside the inner bag.
5. Seal the inner bag with a little bit of air still left in it, and then seal the outer bag.
6. Check back 8-12 hours later, and check the hygrometer’s reading. The relative humidity inside the bag at this point will be exactly 75%. If your hygrometer is adjustable, calibrate and re-test. Otherwise, write the difference (e.g. “add 2%” or “subract 4%”) on the label, and stick it onto the hygrometer. If you don’t have a sticker, you can use a Sharpie™ to write directly onto the body of the hygrometer. (For digital hygrometers, simply replacing the batteries can cause the readings to fluctuate +/- 5%, so you might want to use the stickers instead of using the Sharpie™.)
Some hygrometers have readings that drift up or down over time, so it’s a good idea to do the salt test every 6 months or so to maintain accuracy.
Now you are sure the humidity in your Coolidor is correct. (see related article) CoolerHumidor.html