I mean the actual temperature, which existed before humans had defined it. Maybe another non-circular way to say this is that you will get different results depending on whether you mix 99 parts ice and 1 part boiling water, vs other materials at the same temperature.
If we’re lucky the mercury in our thermometer moves up a constant amount each time, and we can avoid mixing things to calibrate our thermometer in the future. If we’re unlucky it doesn’t and we need to painstakingly calibrate all thermometers. If we’re really unlucky a scale that works on one substance doesn’t work on another and then we need to rethink this whole temperature thing again.
I mean the actual temperature, which existed before humans had defined it. Maybe another non-circular way to say this is that you will get different results depending on whether you mix 99 parts ice and 1 part boiling water, vs other materials at the same temperature.
Or in other words:
In fact you get unlucky on both counts.