Too bad about the TEMPer Hum and thanks for keeping me from buying one. Clearly, that’s WAY off but I think your experience with your other instruments is pretty typical. I’ve found that thermometers are usually pretty close but hygrometers vary widely. My experience has been like Georges, a 10% 0r 15% variation is pretty typical, sometimes more. A couple of years ago I bought three hygrometers for my ukulele cases, ones that are intended for cigars. All three read ~20% low. Before I retired I took one of my “good” hygrometers, a Honeywell, to work and had our aerospace gage lab calibrate it. They couldn’t actually adjust it but they did tell me it’s off by 5% at 50% RH. Assuming it has stayed constant over time (maybe not a good assumption), I can at least factor in that 5% and know what the actual RH is in my “ukulele” (nee dining room) room.

However, I think there are two things going one here. One is that it’s a Good Thing to keep the RH where your ukes live reasonably constant. It’s not so much the RH itself but wide swings that will crack the wood. That said, the other factor is how different your mean RH is than the place where the ukulele was glued up. If George is right and your Koa Pili was built built in a humidity controlled factory in China it shouldn’t have cracked (unless the wood wasn’t properly dried in the first place). Like you though, I had one nice ukulele (a Mele concert pineapple) crack even though I ALWAYS kept it humidified. And when I posted about it I heard from others who had the same experience with Meles. My conclusion was that the environment Meles are built in is just too humid and therefore too different from my home in the Northeast during heating season.

Glad you had a happy ending.

PS - I’m enjoying your Boat Paddle series and looking forward to Jerry starting my BP concert.

Anyway, for humidity reading, most of my cases have a cheap “Springfield” thermometer/hygrometer I bought at Wal-Mart for like $7 each. The humidity reading between them seem to vary by about 10-15%. I also have a couple of thermo/hygrometers specifically made for instruments and a couple that comes with the Ameritage case. All of these return different humidity measurements, but they are more or less within 10-15% of each other, so I get a general idea of the humidity in my cases. I don’t think the instrument-specific hygrometers are any more accurate than the cheapos.

I think the best you can hope for is to get a rough idea of the humidity and put plenty of humidifiers in the cases during the winter. Hope that helps.