I use a digital thermometer with a thermocouple. Drill a hole in a coated bullet. Secure the thermocouple with high heat aluminum tape. Put the t-bullet in with the bullets you are baking. The thermocouple is thin enough it won't affect the closing of the door. Most of my powders are 10 minutes at 400 F. When the t-bullet reaches 400 F I start a timer counting down from 10 minutes. Powder coat has a bhn of 27 to 28 if properly cured. I want that especially for my rifle bullets. I know a lot of you have a system that works for you. If it ain't broke don't fix it. This is another option.