I purchased an Atten 191 soldering iron thermometer which uses K thermocouple elements from Allendale UK.
Above, the Atten 191 on a K thermocouple calibrator. Here you can see that it is reading 76° high at typical soldering iron temperature. It wasn't very expensive, but was total waste of time and money.
The supplier stated that they knew they were a bit out out at room temperature, but weren't too bad at typical soldering iron temperatures.
The reasons that K type thermocouples are wrong at room temperature is that their temperaure compensation element is not calibrated, and that error is an offset in all readings.
The reason they are wrong a long way from room temperature is that the amplifier gain is wrong, poor calibration again.
The supplied sensors have to be untwisted to span the pins on the thing, another quality failure.
It will cost nearly as much to return it by signed for shipping as it cost to buy in the first place (outbound post from Australia is expensive)… a lesson learned about the quality of Atten and Allendale. I have ordered a Hakko FG-100 for about half the price, we will see if that is ok.