Spark Advance/Retard Mechanism

[Diastole]

I am new to Model As.
I am curious as to what is the mechanism for how the lever changes the spark timing?
The distributor is mechanically controlled by the cam. The rotor is set in timing the engine. Neither are adjustable once set. The points gap is fixed, as well.

What action does the lever do to advance or retard the spark?

I understand how to set the lever and when to change it. But, how does it work? What does the lever change in the distributor or the engine to modify the time the coil discharges to create the spark and ignite the compressed fuel/air mixture?

Thanks in advance for help with this illusion mechanism for me