Use or don't use vacuum advance on distributor???????????????????

The advance can on my MP distributor can be adjusted to control when it is actuated. When I insert an allen wrench into the nipple, one full turn in either direction raises or lowers the point of actuation by approx. 1" of vacuum.

I'm not sure if it's the original can or one put on by Don at FBO. Doesn't really matter though because the MP instructions that come with it confirm that's what you're doing.