Checked humidity levels the next day and results were essentially the same as the day before for two dampit style humidifiers in the soundhole. Probe 1 in headstock area read 29%, probe 2 near neck/body connection read 32%, and probe 4 on top of the body near the strap button/output jack read 31%. Probe 3, inside the soundhole, crept up slightly to 43% RH. Ambient room read 30%. Plan to leave these humidifiers in place to see how long they take to dry out.
I also checked hygrometer accuracy by performing a salt test on the probes, and found they're reading a few percent higher than the expected 75% RH. While I might get truer readings by subtracting these amounts from the readout - at least in the 75% range, it's not so clear how this offset scales to lower humidity levels since the relationship may not be linear. For the sake of this testing, and not to over complicate findings, I will report the same values as on the readouts, recognizing the actual values may be a bit lower.
Damon DeBusk is a multi-patented product designer, process and quality engineer, project manager, author, and inventor of Musik Tent Instrument Humidors and HumiForm Cigar Humidifiers.