Measuring PP port timing

[sen2two]

I am checking my PP timing so I can scribe lines for additional port shaping and i am unsure where to mark for open and close on the port.

Does the port open when the apex seal moves past the bottem edge of the port?

Does it close when the seal after that passes the upper edge of the port?

Or is it when a specific porting of the rotor face passes the port?


Heres a picture of my ghetto set up. This is just a test set up. I am going to make a real set up later on. I just need to know if I am doing it wrong...

The mark on the rotor housing (0-) is TDC (Directly between the 2 spark plug holes). The degree wheel (I printed out one from online) and taped to a rear counterweight. The pointer is taped to the rotor housing and is stationary.