I decided to completed the tuning of my wife's Edison with a record playing. A few weeks ago I built the tool shown in the video that I posted on youtube. This was the first time I had measured and adjusted the Edison while under load. The first number in the display is elapsed time in seconds. The second number is the computed RPM. The gadget has an optical sensor that detects the cardboard paper as it passes between the sensor and led. I simply count the number of times it detects the paper and divide by the elapsed time. Nothing fancy. The arduino does not have a realtime clock so it may not be super accurate but when I compared it to me counting the number of rotations for a minute it seemed pretty close.
If anyone wants to know how I made it I'm willing to share. Just let me know by emailing me at firstname.lastname@example.org. You can reply here too but I probably won't visit quite as much now that I have completed the restoration.
You can only get to the video by following the link below.