Back in Gainesville in 1997, I learned how to do this using the chopper wheel. We had to make the assumption that the wheel's blade was moving horizontally during the time of the chop.
One advantage is that the repetitive slices reduces the random errors by a lot - you can trigger the scope and average. Another advantage is that you can download the average scope trace using USB, floppy, or ethernet instead of pencil and paper.
But, I never analyzed it in enough detail to see if there was some kind of nasty systematic error.