thermocouple vs. thermistor
A thermocouple measures the temperature of a point, whereas a thermistor measures the temperature of an area. The thermistor here has been calibrated using the thermocouple. So they may just be measuring different things. That said, they’re pretty close.
Relative temperature is more important than absolute temperature. If relative measurements are correct (i.e. the difference between successive readings) then the temperature profile that produces a good result will be repeatable.
