The daiso meter is pretty accurate. Atleast for mine. It is okay for it to have some deviation. About +/- 5%. It applies for even expensive hydrometers. Btw my daiso bought one is from bukit panjang. Mine lives permanently in the dry cabinet after i bought one.
Response time is more of an issue than accuracy. Analog ones take some time to change to new humidity.(eg. When i open the door of the dry cabinet humidity rises sharply with electronic one, while analog one slowly increases). Opposite applies for closing of dry cabinet door.
Btw i opened the daiso meter's cover before. Inside is just a coil of flat copper-colored wire, attached to the middle axle for the display needle.
Hygrometer made and shipped will never be 100% accurate. Calibration is usually required even for expensive model. Each time you do the controlled salt test, wait 8 hours and observe where the needle is pointing.
It might likely be not pointing at 75% but at other readings instead. All you need to note is where it is pointing. That is the 75% mark. If you repeat the test and it always point at the same place. Just adjust the needle to point at the 75% mark BUT if there is no adjustment screw available to adjust the needle, then try to rotating the reading dial till the 75% mark is at where the needle points. Put it in your cabinet and see how much difference it is compared to the digital hygrometer of your cabinet. Your salt tested hygrometer will show you how accurate the digital one in your cabinet really is... or not.
If you can not adjust the digital one, then just mentally offset the difference to figure out the true reading of humidity in the cabinet. Hygrometer is old tech so even the cheap type will still be quite a good indicator for reference. Non digital ones that is. So long as you keep the humidity of your cabinet within the optimum range you are fine. Mine stays within 33 to 44% when I keep opening and closing it often. When I never open the cabinet, it stays around 36%.
I use that for all my photographic gear and electronic devices without problem for years.
Last edited by sammy888; 22nd December 2015 at 01:06 AM.
A good photo's 45% you, 45% practice & 10% equipment. A bad photo share the same ratio.