Billboard Hot 100
A basic example is the weight given to sales versus airplay. Initially, singles were the leading way by which people bought music. When singles sales were robust, more weight was given to a song’s retail points than to its radio airplay. In later decades, the recording industry concentrated more on album sales and musicians eventually released more full-length albums than singles, and by the 1990s many record companies stopped releasing singles (see Album Cuts, below). Eventually a song’s airplay points were weighted more than its sales. Billboard adjusted the sales/airplay ratio many times to more accurately reflect the true popularity of songs.