Temperature seems difficult to measure accurately. I worked at a plant in instrumentation. The processes required the temperature stayed very stable at around 250 to 350 deg C. The absolute value did not mater, but once the process was stable then the temperature was kept at that setting. We could measure it to two decimal places at 300 deg C. However they could be off as much as 2 deg C at 300 deg C. This was with instruments costing in the thousands of dollars.