Here in the midwestern US it's our annual crack season where lots of acoustic guitars that are not kept humidified will crack and need repair.
One of the very best ways to avoid cracks and having to visit us if you are not skilled in repair is to humidify your instruments.
I've written much on RH and hygrometers on this forum and others over the years and previous threads are available for those interested in searching for same.
My annual ritual at my house it to get out the psychro-dyne and run several tests comparing the wet/dry bulb results to what the hygrometers indicate and then either adjust the hygrometers or annotate on them the error rate.
Some back ground: I've yet to test a digital hygrometer that is accurate and as such even when they are accurate when new the electro-chemical reaction that digitals depend on also breaks down over time and the hygrometers drift often a great deal. We've also tested digitals that may read pretty close in a certain range, say 40 - 50 but may be 10% or more off above 50% or below 40%.
Conclusion - digitals are junk.... YMMV.
A word about the standard that we use. A Psychro-dyne is simply an implementation of the wet bulb test which can be done also with two thermometers or a sling psychrometer. In our experience any wet bulb test done correctly will be WAY more accurate than any hygrometer that we might purchase sands the multi thousand dollar offerings.
I'm going to post some rather poor pics, forgive me please my Photoshop is not working so they are not edited and off an IPhone.
You will see on some of the crappy digitals that I annotate the error rate. I've crossed off last year's error rate and replaced it with what the tests provided me with this AM. Both digitals have brand new batteries as well.
Interestingly enough a little $8 mechanical hygrometer that I picked up last year just to check it out is again, just like last year, the winner for accuracy. Go figure...
So if you are looking for an accurate hygrometer the mechanical one pictured is currently recommended for the budget crowd. When you are inclined to spend more the Abbeon Cals are excellent and my standard for my home. My Abbeon was about 3% off this morning and I adjusted it to be calibrated and that will get me though the year.For new builders maintaining a proper RH range is so very key to acoustic guitar building, important for electrics as well, that it should be job one when outfitting a shop. Ignore RH requirements and you will be building time bombs in terms of instruments that will not hold up well with RH swings in the future.
It's important, an understatement.
Hopefully my reminder and some of the information here will be useful to our OLF pals.
And I got the like-new Psychro on eBay for next to nothing.
and when I get home in the evenings the cycle repeats too....