One thing needs cleared up here. The vacuum advance may be adjustable but not the amount of degrees it advances. That allen adjuster only affect when it advances. The amount of vacuum that's needed to pull it in if you will. Like DGC said he has his set to get full vacuum advance at 14 inches of vacuum. If the vacuum can has 10 degrees of advance it'll always put in 10 degrees of advance no matter what the allen screw is set at. Also consider this, double the vacuum advance's rating to get the amount of degrees of advance at the crank so a 10 degree can will produce 20 degrees of advance at the crank.