And wasn't based on actual monitored airplay, but rather reported airplay.
When AT40 started, airplay was not part of the Billboard charts. It was mostly record distributors, one-stops and the like.... the wholesale step of the record business. IIRC, it did not include retail.
Airplay is what got Gavin started, later spawning Hamilton, FMQB and the rest... and by '77 R&R.
And that was the issue. Record companies, always the paradigm of ethics and responsibility, would push huge quantities of a song into "the channels" and thus get a big chart bounce, hoping for "with a bullet" in the next chart and knowing that those chart jumps caused both radio and retail to push a song.
Those songs that had a big chart burst and then disappeared in two weeks were ones that had been subjected to that practice. I know that some of those pushes brought a song home, so it must have been worth it to the labels but it made the charts very suspect.
When I was in Puerto Rico in the early 70's, two stations called the bigger record shops and got sales reports each week. We discovered that via a "he had a couple of drinks and spilled the beans" episode and switched to rotating small record shop reports, skipping the big guys. A couple of T Shirts and the like tied that up, and our reports were really different from "theirs". The next book, we beat them.
Of course, it was amazing to see how charts changed when we began to have detection-based charts instead of station reported airplay.
To them, it is all about a three word vocabulary: "Play my record".
