A basic example is the weight given to sales versus airplay. 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.