462" Buick with Mallory Unilite vac adv distributor and MSD 6AL.

My Sears Penske timing light (standard model) reads right on as confirmed by static timing the engine.

I tried a Sears Penske dial-back style timing light and it read 20 degrees off - I think on the retard side, but don't quote me.

I've mentioned this on other boards and the replies have been that some dial-back lights don't read right and others do.

The dial-backs are nice, but a degreed balancer - which I now have - or a timing tape will do it.