A thermometer can help you establish a more consistent roasting routine. Adding a thermometer to your air popper measures the temperature of the forced air heat flow after it has passed through the beans.
This is the back of our Probat L12 roaster. It's the part of the roaster that doesn't get any sort of spotlight, but is just as important in creating the magic. Those chains provide power for the airflow, drum and cooling arms so they are pretty darn important.