http://www.centuryperformance.com/vacuum.aspA must have diagnostic device in the tool box.
Great for engine tuning too.
Short of being an expert engine rebuilding auto mechanic you need some knowledge just for tuning, that is the easy part, providing you have a healthy engine.
And if you live in the Rocky Mountains, expect lower readings, One HG per 1,000 feet above sea level, according to John Washburn, the Rocky Mountain man Cadillac expert.
He is well isolated but in demand for vintage Cadillac repair.
Porter