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Likely you have the DELCO EST system (aka Voyager)...the advance curve is controlled by the module and is not adjustable. the module has two connectors: the two pin connector goes to the coil and the four pin connector goes back into the wiring harness.
It is best to set them so the max advance is correct and live with the initial timing...
the timing tab will have numbers "inside" the V's..you might try wire brushing it or just get a new one...they are different on counter rotating engines.
if the timing is NOT being advanced by the module, as the engine's RPM increases, then you need to replace the module first.
Once the timing is advancing ok, then I'd suggest setting the timing, at max advance, to the specified value. You then live with the timing provided by the module at all lower RPMs.
How you set the timing is driven by the equipment you use...some prefer the basic timing light, some prefer the newer "advance" style.
Timing "advances" as the engine rpm increases because it take a finite amount of time for the air/fuel charge to burn...so advancing the timing means the spark occurs even further before top dead center.