A few years later, he had the most clean and consistent pronunciation out of anyone I'd been in a class with, and easily switched between the Beijing and other accents depending on which teacher we had on any given day.
I rather regret not emulating him, even though I haven't really used it for nearly 20 years and have forgotten most of it.
I used simple index finger motions to mark tones.
Highly recommend taking a look at Phonemica for this: