Vacuum Advance
Vaccuum Advance is a purely mechanical method for varying the amount of Spark Advance based on engine load.
Adapted from pgmfi.org wiki
Vaccuum Advance is a purely mechanical method for varying the amount of Spark Advance based on engine load. A vac-advance distributor is connected to a source of engine vacuum. As vacuum increases, forces of suction rotate the distributor, creating more ignition advance. The ECU cannot control timing at all with a vacuum advance distributor.
Credits and source
Source Adapted from Vacuum Advance on pgmfi.org wiki. Licensed under CC BY-NC-SA 1.0.