I'm relying on the temperature from a Brinsea digital themometer, but the Caliber III has been within a degree of the Brinsea's temperatures, registering temperatures as high as 102 (while I'm trying to set the hatcher temperature). Not too bad.
I just bought a digital Caliber III hygrometer on Amazon meant to be used in a cigar box. It says it doesn't need to be calibrated, and I believe it is fairly accurate, although I don't have a known accurate hygrometer to compare it to...