No way for us to know from here which is real but ...
1. Take a bottle cap large enough to fit a couple of tablespoons in. Make sure it’s clean.
2. Put 1 tablespoon of table salt (non-iodized) in the cap, with a coffee stirrer, stir the salt while adding small
amounts of water until it becomes a thick paste. You DO NOT want to disolve the salt with water, just make a
3. Put this cap and your hygrometer in a tupperware or air tight container for 8 hours. After 8 hours it should
read 75%. If it doesn’t then your hygrometer is off.
4. For analog hygrometers, ones with needles not digital read outs, there should be a screw in the back where
you can adjust the needle. Adjust it to 75%, then you’re done. Make sure you have the tools necessary before
pulling the hygrometer out of the container so it doesn’t change while you’re looking for tools. If it’s a digital
hygrometer most don’t have adjustments, so I just tape a small piece of paper to it with the amount it’s off. i.e.
+4 or -3. That way if it reads 70 you’ll know it’s really 74% or 67% or how much your is off.