To be perfectly honest if the thermometers are as close as that I would not worry about it. C41 has a reasonably wide latitude when it comes to processing it at home. I use a JOBO rotary processor and I am quite sure the temp does not stay at the desired 38 degrees C for the whole of the developing period. Even my two precious mercury thermometers which are guaranteed to be within +/-.2 of a degree C and likewise my electronic digital one when in a jar of water agree but outside in the same area on the bench there can be up to 1 degree difference. Just ignore the difference and get on with developing your films.

I am friends with the owner of a local mini-lab and he has told me in the past that his machine sometimes varies as much a 2 degrees all depending on the ambient temp outside.