How to - Hillbilly Timing Tape

I was totally wrong! Trying to reply, while baby sitting an active 3 yr old.
#1 fires every 2 engine revolutions. That time divided by 720, times the desired set back. Same formula. Doing that with uC is easy, analog means sounds iffy.
Never used or owned a set backing light.

Systems I build and use measure RPM based on reference sensors, calculate ignition timing and coil charge for every ignition event. Timing is available in car, and logged for analysis. I only use a timing light to verify static timing. My sensors trigger at zero speed, so not errors related to variable reluctance triggers.