Due to the microprocessor installed and the sensor mounted at the top of the roaster base where you install the roasting chamber.
NTC Thermistor mounting
It appears that when you turn the roaster on to High and lower the fan knob to the lowest setting the roaster will reach (unloaded) 430 degrees. At that point the fan automatically revs up slightly (possibly due to the heater being off) and the heat stops climbing at 433 degrees. Occasionally it drops sooner but always between 430 and 433. It then drops from 430ish degrees down to approximately 420 degrees and then resumes climbing again. The heat appears to always stop at 420 and then goes back up. The highest it stops dropping at is 422.
Temperatures were measured with a new K type thermocouple mounted approximately where the center of the bean mass would be. I obtained this at OSH (Orchard Supply Hardware) since I needed some sort of multimeter for the moment. They had one inexpensive “Craftsman” model with the ranges I need for measurements with the Digital Multimeter side with an included K type thermocouple mode. I’m expecting the thermocouple to not last very long due to the temperature rating they put on it. I will likely get one from eBay or something that is compatible with the K thermocouple sensors in the meter. I’m guessing the protective covering they put on the tip end insulation area to keep the insulation from unraveling is not able to withstand the high temperature for very long but the insulation looks like it can take a lot more. I’m going to probably get some high temperature silicone and put a little dab right at the end above the tip to hold the insulation better so it won’t fray.
Ultimately I’ll source out a thermocouple that can do more properly as I get further into this. I’m going to switch to using the previous thermometer as a timer (was a secondary feature… you get one or the other on screen at any point in time) and the thermocouple as the new temperature sensor since it actually responds faster on temperature changes.