Setting vacuum advance

Mattax, completely wrong. But I should have explained spring 'rate' more clearly. As for not 'seeing inside a Chrys dist', I was reworking them probably before you were worn....I still have a couple of cast iron dists on the wall, do you know how old they are?
I notice Halifax shops hasn't chimed in......That is probably because he DOES know how the vac adv works.

Mattax, you obviously have never pulled apart an adj VA unit. I have, many times. The GM & Chrys adj VA units internally, are exactly the same design, only the method of attachment to the dist body is different. They may use a different spring because of the different leverage ratio.
For those following this who might still be non-believers & have a dist with an adj VA unit, do this simple test: put the dist in a vice. Turn the AK fully CW. Then, with a screwdriver, push on the VA plate; it will move fairly easily.
Now turn the AK fully CCW & push on the plate again with the screwdriver. It is much harder because you have compressed the spring, & you are pushing against the compressed spring. The AK adjustment changes the rate of apply [ or un-apply ] of the VA unit. With the spring set to the softest setting, the plunger will move with less engine vacuum than with the spring set to a stiffer setting. This was the rate I was referring to in post #13.