Thanks guys for the help, I forgot to add that the distributor is a HEI (non-points) distributor.
So the timing gun that I have is an Actron Digital CP7529.
There are several options...
1. Measuring Engine RPM
2. Setting Initial Timing
3. Checking & Measuring Centrifugal Advance
4. Measuring Vacuum Advance.
So what is the purpose and difference for those`?
Appreciate the help, guys.