Insertion distance.

I read somewhere that the warmest place in the body is just one inch inside the anus, and that this is how far a thermometer should be inserted to get the most accurate reading. That being the case, what is the justification for inserting the thermometer much further than that?

I read a number of older medical books, for babies It’s a half inch, for kids It’s an inch and for teens and adults It’s about half the length of the thermometer about 2 inches. I’ve had people say that that’s wrong, but I believe my mom and my grandma believed in those distances as well.

A multichannel DAQ with 14 or 16 bit resolution and a few thermocouples should resolve the question. Considering the protection the perennial area enjoys it would be less influenced by ambient conditions than the face or arm pits. A further observation would be the thermal conductivity of the tissues, and that would lead me to believe the localized differences would be small.