My chart from a old Ford training guide says :
Governor weights spread as speed increases thereby advancing spark.
The same vacuum force that operates your windshield wipers also retards the ignition spark.
As i run one of these almost every day on a machine. I would explain it like this:
Engine off leather brake holds the advance ring by spring tension causing a slight retard in timing allowing a easier start.
Once the engine starts vacuum pulls brake off the advance ring allowing a proper advance as soon as the engine starts.
Driving down the road and hitting a hill (increase load) vacuum will drop off causing a retard to timing preventing spark knock.
There are some good pictures on our web site
http://www.bubbasignition.com/crab-42-48.html
I guess its how you word it?????