Thanks and yes, that pretty much sums things up. Years ago the vacuum of work sucked me more and deeper into temperature than I ever wanted to go. Long before many of today's reference standards for temperature existed.Nice explanation Ron, thanks.
The only thing I can think of to add is that all this relates to the temperature *of the thermocouple junction*. How close that temperature is to the temperature that you *actually want to measure or control* involves a whole lot more assumptions and possible sources of error. In almost anything other than a well stirred liquid, there are almost certain to be temperature gradients due to heat flow, including heat flow along the probe itself...
You make a very good point as to what I called a thermal bath, typically filled with an oil similar to automotive anti freeze. The bath could be set between -20 F. and I think 400 F. The test thermocouples were bundled with a PRT Standard and placed in the bath. The bath had a circulation pump to eliminate any thermal layers. The output voltages of the thermocouples under test were measured and recorded over a range of cardinal points. There was more to it but that's it in a nutshell. Temperatures above the bath limits were done in a small furnace which we typically did up to around 2,000 F. (Thermocouples used in large furnaces for uniformity test). Temperature measurement can really get into some interesting stuff.
Ron