I think the offset is right on mine from a crude test, just a wire probe over a blind basket I held close to PF for ~5 sec... temp on Omega meter showed exactly what PID displayed.

Very OT, sorry... but this thread made me think of it. I've had fantastic results lately at 194F. It made me wonder how low I can go... so tried 192.... definite sour!! It's interesting my favorite temp is so close to the sour edge. I guess I have my trial range now... 194 - 202 or so...