This graph compares the raw MK5 thermocouple temperature against the adjusted reading from the Fluke 52 T2 thermocouple.
The regression line says the slope matches to within 0.01 °C and the offset is less than half a degree. While the line is a bit bumpy, that has more to do with the hasty data-taking than anything else: the points corresponding to the last reading at each power level are very close to the line.
Given that the adjustments to the T2 readings make them match the average of five thermocouples, not including the MK5 unit, I’d say the MK5 is spot on.
This doesn’t affect any of the conclusions I’ve come to over the last few days; I always put the MK5 thermocouple bead in a non-critical location.
Based on the earlier measurements, the Thermal Core seems like a reasonably isothermal setup. That means the reading displayed in the ReplicatorG control panel accurately reflects the Core temperature.