[hvychve]

The wheel on the back of the light is usually for checking advance, ie. vacuum and mechanical advance, if you were to check your timing while holding RPM's up, you would see your timing mark move, so to move it back to where it was before you reved up engine , you must turn the dial, if you remove the vacuum advance before you do this, you will be checking the mechanical weights under the rotor (mechanical advance)and when you rev it up w/ vac. advance on this will give you total advance, I hope I didnt confuse you , however, if you were to run your engine with pickup lead (inductive probe) on cyl. #1 start engine (warm) off fast idle, you could do it either way, you can dial your light to read whatever you want timing at, if for instance you wanted twelve degrees, and you had dial on tiiming light showing twelve degrees and your mark on balancer was aligned with zero, you are actually 12 degrees, also you can have your dial @ 0 degrees and the mark on balancer could be showing twelve degrees, that too is the same..... hope this helps.....