The Billboard charts tabulate the relative weekly popularity of songs and albums in the United States and elsewhere. The results are published in Billboard magazine. Billboard biz, the online extension of the Billboard charts, provides additional weekly charts, as well as year-end charts. The two most important charts are the Billboard Hot 100 for songs and Billboard 200 for albums, and other charts may be dedicated to a specific genre such as R&B, country, or rock, or they may cover all genres. The charts can be ranked according to sales, streams, or airplay, and for main song charts such as the Hot 100 song chart, all three data are used to compile the charts. For the Billboard 200 album chart, streams and track sales are included in addition to album sales. The weekly sales and streams charts are monitored on a Friday-to-Thursday cycle since July 2015; previously it was on a Monday-to-Sunday cycle. Radio airplay song charts, however, follow the Monday-to-Sunday cycle (previously Wednesday-to-Tuesday). The charts are released each Tuesday with an issue date the following Saturday. History The first chart published by Billboard was "Last Week's Ten Best Sellers Among The Popular Songs", a list of best-selling sheet music, in July 1913. Other early charts listed popular song performances in theatres and recitals in different cities. In 1928, "Popular Numbers Featured by Famous Singers and Leaders" appeared, which added radio performances to in-person performances. On January 4, 1936, Billboard magazine published its first pop chart based on record sales. Titled "Ten Best Records for Week Ending", it listed the 10 top-selling records of three leading record companies as reported by the companies themselves. In March 1937, the "Songs with the Most Radio Plugs" chart debuted with data from a separate company. In October 1938, a review list "The Week's Best Records" was retitled "The Billboard Record Buying Guide" by incorporating airplay and sheet music sales, which would eventually become the first trade survey of record popularity. In the July 27, 1940, issue, the first "Billboard Music Popularity Chart" was published for week ending July 20, with separate listings covering retail sales, sheet music sales, jukebox song selection and radio play. Among the lists were the 10 songs of the "Best Selling Retail Records", which is the fore-runner of today's pop chart, with "I'll Never Smile Again" by Tommy Dorsey its first number one. The final accolade of a successful