A record chart, also known as a music chart, is a method of ranking music judging by the popularity during a given period of time. Although primarily a marketing or supermarketing tool like any other sales statistic, they have become a form of popular media culture in their own right. Record charts are compiled using a variety of criteria. These commonly include sales of records, cassettes and compact discs; amount of radio airplay; requests to radio disk jockeys; voting for songs by the radio listeners and, more recently, number of downloads and streams.