After tweaking the Kp and making the Ki work in the software the graph speaks for itself. The software is controlling the temperature to the set point of 140°F within a fraction of a degree for the most part. This was the last difficult piece of puzzle. I did not use the PID function in the Arduino language, instead I wrote my own with a large part of the understanding of the code coming from the excellent description by Brett Bueargard who wrote the PID library, as well as assistance from a friend who helped me understand the problem better in a spreadsheet. I now have a burner that works dependably and is modular so that I can make changes and see if I can further improve the efficiency. I now have software which will hold the temperature without worry. I plan to add a proof of fire sensor next for the mechanical part of the project, and add the ability to set the Real Time clock in the software. Onward, ever onward, but for today I think I will have a beer!