I left a line of product as a visual guide for before/after. Obviously the section on the bottom is the before.
This is why correction is an art form. There is no "formula" set in stone. It is really important to do a test section and figure out what combination of product, machine, pad, technique works for the vehicle.
Every single vehicle is different, and even different panels can be different. Test, assess, react, re-assess. Once the formula has been found that works go to town on the rest of the vehicle. Take your time, this is a slow and labor intensive process.