The Aircraft Magneto Timing Light Model E50 is the industry standard. Designed specifically for the internal timing and synchronization of aircraft magnetos, the E50 safely absorbs the current from the magneto's impulse coupling -- so there is no danger of engine firing while adjustments are being made.
The E50 timing light takes all the guess work out of the magneto timing process. And it's quick and easy to use: simply attach the three clips to the magnetos and adjust them until the E50's two blinking lights are synchronized and the buzzer changes in pitch. That's all there is to it. Perfect timing.
I have used this exact make and model timing instrument for over forty years and when leaking battery caused problems, i looked for and replaced it with the same E50 that has only changed their tone of alert as far as I can tell, all else is identical. I have every confidence that the new one will still be working when Im gone in another forty years or so.
Veru easy to use, just bought this item, and it works as advertised. Checked my Bendix mags on my IO-540 Lycoming and both were sycro'ed nearly perfectly after using the E50.
Per the supplier: yes, it will work on a single case, dual magneto set up.
No, per the manufacturer, they do not require calibration.