digital hygrometers, by factory specs, can have a + or - 5% error. radio shack has the most reasonable prices, so buying one just gets you a more expensive, made in china, device, that has the same + or - deviation.
when you do the salt test, the easiest way to deal with the deviation is by marking the deviation on the hygrometer with a marking pen, ie +3 or -2. subtract or add the noted deviation and that will tell you where you hunidity really is.
if you want to tinker and are a little handy, the pot can be adsusted. if you don't know what a pot is, you are probably best using the above method.
if your curiosity has taken hold,
RICKAMAVEN@
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