My goal is not to determine the exact reasons for different performances between units. I'm merely trying to verify that TM units can differ from each other by quite a lot regarding the temp dial setting versus actual temp,
with the difference being due to internal/inherent components or properties (like the ones you mentioned: the electrical circuit, resistance variables, etc). I was trying to rule out the "external" variables that we all bring to the table: strains, packing, draw speed, distance from load to heater, etc.
Probably an exercise in futility. Disregard if desired.