"Advance Curve" Kind of a misnomer here. You are talking about initial and total advance only.
The "curve" would be a graph showing how many degrees at different RPM's until you hit the total.
How many degrees at 2500 rpm, 3000 rpm, etc...There are slow curves and quick curves. These were done on a Distributor machine off the car using different weights, springs, slot lengths, different Vacuum advance units.
More to the story... Quick Tech: Why You Still Need Vacuum Advance
