I just bought a hygrometer from Walmart to make sure my guns and ammo are being stored in a proper environment with low humidity. For those who don't know, a hygrometer tells you the relative humidy (RH) which is a number between 0 and 100%. Well I bought this from Walmart:



And as you can see its already back in the package, ready to be returned to the store. I did a salt test right after I purchased it, which is a way to tell how accurate the unit is. Its really simple. When salt and water are combined in a sealed container, the resulting RH is 75%. That number slightly fluctuates depending on the temperature, but by such a tiny amount that we can completely disregard it. So all you have to do is put some salt and water in a soda cap, and put it in a sealed container along with the hygrometer, and wait about 8 hours. If your hygro reads 75% RH, then you are good to go.

Well I tried this using a ziplock bag, and after 8 hours my hygro read 68%. So I waited another 8 hours. Still 68%. Then I thought I would try the experiment again, but this time using a mason jar and using new salt and water. After 8 hours it was at 69%, and at 16 hours it was going back and forth between 69% and 70%. Obviously something was wrong.

So I opened up the unit and noticed that there was a solder pad that was ripped off the PC board, and the main element of the unit was instead soldered to one side of a resistor that was in series with it. The result is that the electrical path was the same, but the inductance of the circuit was changed. Someone on the assembly line screwed up and did a hack job to "fix" their mistake. I called the manufacturer about it and they denied that it was assembled wrong, and told me I could fix it by taking the battery out and putting it back in. Needless to say I'm not even trying that, and this unit is going back to Walmart. I'm very disappointed, but I guess thats what I get for shopping at Chinamart. I will be looking for a unit made by a different company that is capable of proper calibration.