@Yale-E-Goldman: I had problems with configuring UNO as ISP. It was long time back, so I don't remember the exact error codes, but I remember that the UNO programmed using IDE 1.6.x to act as an ISP failed to program the "3rd" UNO. All versions of IDEs are not good for the job. Finally, I was able to program the 3rd UNO using the 2nd UNO (ISP) which is programmed into an ISP using the 1st UNO with IDE 1.0.1. https://www.instructables.com/Burning-the-Bootloader-on-ATMega328-using-Arduino-/ I still have that ISP UNO, and it can work as ISP with other versions of IDE such as 1.8.x Thanks..