Vacuum Guage Readings

A previous,but related thread posted by Mullinax 95 on Compression test??? and Street Demon's reply about a leak-down-test got me thinking about another way of checking the health of an engine. I got out my Chilton's manual and looked up the section on vacuum guage readings. After hooking up a vacuum guage on the intake manifold beyond the throttle plate, note what the needle does on the running engine. Depending on its movements and what they mean (interpreted from the manual) you would know where to start looking for the trouble. A leak-down-test would surely pinpoint the problem and confirm the vacuum guage readings.
In addition to just using the vacuum guage as a problem diagnosing tool, one could have it to monitor an "engine's health" on an ongoing basis plus it can be used as a gas mileage monitor. This gas mileage monitor is something I want to do with my Dart. On some Mopars (somewhere around 1970) some were factory equipped with a vacuum guage. When you stepped on the throttle pedal too hard, a light would come on from a signal light mounted on the front left fender. If anyone knows of such a device I would be interested in getting one.
Great forum and by what I'm reading on various posts, very knowledgeable people here. Good to be part of the group.