List of record charts  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, recently, number of downloads. Some charts are specific to a particular musical genre and most to a particular geographical location. The most common period of time covered by a chart is one week, with the chart being printed or broadcast at the end of this time. Summary charts for years and decades are then calculated from their component weekly charts. Component charts have become an increasingly important way to measure the commercial success of individual songs. Reviewers often describe records using round number milestones within a chart. For example, a record that peaks at number 7 may be called a "Top 10" hit, even when there is no chart limited to only the top 10 records in that particular location. The following books list recording artists in alphabetical order unless otherwise stated.