The original formulaic radio format was Top 40 music, now known within the industry as contemporary hit radio or "CHR". In this radio format, disc-jockeys would select one of a set of the forty best-selling singles (usually in a rack) as rated by Billboard magazine or from the station's own chart of the local top selling songs. In general, the more aggressive "Top 40" stations could sometimes be better described as "Top 20" stations. They would aggressively skirt listener boredom to play only the most popular singles.