This 2-stroke engine timing gauge tool answers this question in a simple way. 

You will find an explanatory tutorial below. 

With the timing gauge tool, you will be able to easily hold an internal rotor ignition on 50cc. 

You will be able to set absolutely any type of ignition. 

In order to facilitate the reading of the calibration, the gauge is graduated from 0 to 9. 

This means that one turn off the freelance head represents a 1mm calibration. 

1 scale therefore represents 0.1mm. 

If, for example, you want to set its ignition to 2.25mm before the TDC (top dead center), you will have to screw in the head 2 turns + 2.5 graduations.