Fair point Dean. The M21 mag changed postwar from MO1 to MO1L though I'm not sure if the manual cable entry point changed sides.
When viewed from the Points side a clockwise rotation mag with a left hand cable entry will be fully advanced with a slack cable and vice versa.
The confusion arose from Bernie j's reply where he states he hardy ever uses full advance.
After forty five years experience of motorcycle maintenance, restoration, competition and road use I have yet to see a engine that has overheated or burned a valve due to running the correct ignition advance.
Changing the subject slightly, do any members have experience of using EasyCap condensors and are they available for
lucas face cam type mags ?