I process 120 and 35mm film in stainless steel inversion tanks, typically Tri-X shot at ASA200, D76 1:1, 7 min to 10 min (depending upon contrast) at 68 degrees. I presoak at 68 degrees and keep the tank in a tray of water at 68 degrees during processing to help maintain the temperature. I am very careful with these steps and measure and record the developer temperature as it is poured from the tank. Inevitably, the temperature drifts higher (never lower) following these procedures. Sometimes it is 1/4 degree, other times as high as 1 degree especially during the warmer months when the darkroom may be as warm as 80 degrees. Even in the dead of winter when the darkroom is perhaps 68 degrees, I get a small drift in temperature. My question is whether some of this drift is a byproduct of the development process?