Thanks much, that's over my head.
Dave
The cold junction compensation bit? That is not hard to understand at all.
The "temperature sensors" used on these soldering iron tips are thermocouples. A thermocouple reads a difference in temperatures not the absolute temperature, so in a iron tip it measures the difference between the tip temperature and the ambient temperature (not so simple but close enough). So in order for you to know the real iron tip temperature you need the thermocouple measure and another sensor reading which can provide the ambient temperature. Than you just compute the tip temperature real temperature.
Now you can ask what is the real value of having the ambient temperature being displayed, and you are right it isn't critical, I see it more like a sanity check, if it is on the ballpark of the ambient temperature it means the cold junction temperature sensing is at least reading something close to reality.