Ok I bought a timing light the other day. Whats the difference between a normal timing light and an advance timing light with the **** on the back?

 

An advanced light just allows you to set the number of degrees advance you want on the gun and flashes at that advance. If your marks don't line up you know your timing is off. A gun without the flash advance requires you to move the distributor first too your marks to get a reading and the flash on the marks indicate the amount advance not a scale on the gun.