I remember those things, along with similar ones on other makes as well. Some had a green/yellow/red light, others had a "fuel economy gauge" which was just a vacuum gauge with 3 colors and markings like good, marginal, poor, instead of numbers.
Interesting to read about. Too bad it was written by someone who doesn't seem to have a clue what cars were like back then since they all had some sort of gimmick like that.
I thought that too. The author obviously wasn't born until 30 years after that era. His holy grail Japanese cars had the same type of thing in one form or another.
My mother had a 1975 Newport with a feature that had a vacuum switch wired into the upper fender turn signal lamp that operated the light as a fuel economy light . It was a 4 door sedan with a 360 A-block in it.
Never heard of it until today. It appears to be a gimmick to get more money out of a terrified public during a fuel crisis. Early A Bodies had the "Performance Indicator" that was nothing other than a vacuum gauge. I have one on my 67 Barracuda. Any gear head can use a vacuum gauge to improve fuel economy. Seems like it had a red light that illuminated when you floored it (I could be mistaken). Remember the 4-6-8, the Oldsmobile Diesel and other disasters of the era? At least this worked.