The Billboard charts have long been considered the standard for measuring the popularity of records in the United States. The first chart, a "hit parade" was first published in 1936. In 1940 this became the "Music Popularity Chart." In July of 1940, the "National List of Best Selling Retail Records" was published, the first chart based on a nationwide survey of record sales. When the Elvis Era began in 1956 Billboard had four charts that reflected different aspects of record's popularity: Best Sellers in Stores, Most Played By Jockeys, Most Played In Juke Boxes, and the Top 100.
During the Elvis Era the charts went through some changes. The Best Sellers In Stores, Most Played By Jockeys, and Most Played In Juke Boxes had been in use for decades, but the Top 100 had debuted in 1955 in an effort to reflect the combined popularity of the records. Considering the decline in the use of juke boxes in comparison to radio play, the Most Played In Juke Boxes chart was discontinued in June of 1957. In August of 1958 the Hot 100 chart first appeared, combining all aspects of a record's popularity. When referring to years prior to 1958, most researchers have used the Best Sellers in Stores as their reference.
While today, the Billboard charts are calculated based on the use of Nielsen Sound Scan tracking, during the Elvis Era data was gathered by reports filled out by radio stations and stores. The number of spots in the rankings varied from 25 to 100. Often times a record would fall off the chart rapidly because the stores / stations would stop reporting a record's use when the label quit promoting it.
Billboard also published a "Rhythm & Blues Records" chart and a "Hot Country Singles" chart during the Elvis Era. One of the major distinctions of the era was the "cross-over" of songs from these two charts to the Hot 100. Indeed, the rock and roll genre was born from the crossover of R & B and country into main stream America.
Below are the three charts from January 26, 1957. While the "Best Sellers" and "Played by Jockeys" lists are fairly similar, the "Juke Boxes" chart had some signigicant differences. For example, "Just Walking in the Rain" was #5 on the Juke Box list, but wasn't in either of the other two top tens.