Billboard Hot 100
The advent of a music single song chart spawned chart historians and chart-watchers and greatly affected pop culture and produced countless bits of trivia. The main purpose of the Hot 100 is to aid those within the music industry – to reflect the popularity of the "product" (the singles, the albums, etc.) and to track the trends of the buying public. Billboard has many times changed its methodology and policies to give the better reflect what is popular.