Leading & trailing edge of dist chopper & firing point

[Circlotron]

The chopper wheel in the VP distributor has vanes about 40 crank degrees wide and gaps about 50 degrees wide. When the ECU is disconnected the spark occurs at the leading edge of the vane, as far as I can tell. When the ECU is operating, where is the reference point from where the delay is counted from till it sparks. Is it the previous leading edge (90 degrees ahead) or the previous trailing edge (50 degrees ahead)? If it is the former, does the trailing edge have any say in things?

[Jayme]

leading edge in module mode, trailing edge in EST mode. add on the 10 deg advance at the dizzy and they are 10 deg BTDC and 60 deg BTDC and this is why the ref angle is 60 deg. the ECU then knows that when it receives a ref pulse from the module that is 60 deg BTDC, it then counts and tells the module when to fire to acheive the target advance. so yeah your trailing edge is critical.