Distributor: Description and Operation

Fig. 1 Breakerless distributor w/Hall transmitter:

The distributor, Fig. 1, contains a slotted rotor mounted on the distributor shaft and a Hall effect switch mounted on a plate inside of the distributor. The distributor has both vacuum and mechanical advance mechanisms.
The vacuum advance is a dual diaphragm unit. The second diaphragm is used to reduce pinging when the engine is under turbo assist.