Music sales rankings by the trade magazine Billboard
Billboard logo
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,[1] as well as year-end charts.[2] 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.[3] For the Billboard 200 album chart, streams and track sales are included in addition to album sales.[4]
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).[5] The charts are released each Tuesday with an issue date the following Saturday.[citation needed]
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.[6] On January 4, 1936, Billboard magazine published its first pop chart based on record sales.[7] 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.[6]
In the July 27, 1940, issue, the first "Billboard Music Popularity Chart" was published for week ending July 20,[8][9] 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 (featuring vocals by Frank Sinatra) its first number one.[6][9] This best-seller chart (also known as "Best Sellers in Stores" and "Best Selling Pop Singles in Stores") is considered the true guide to a song's popularity until the creation of the Hot 100 in 1958.[10] Another accolade of a successful song was a position on the "Honor Roll of Hits", introduced in March 24, 1945, initially as a 10-song list,[11] later expanded to 30 songs, which ranked the most popular songs by combining record and sheet sales, disk jockey, and jukebox performances as determined by Billboard's weekly nationwide survey.[12] This chart amalgamated different records of the same song by different performers as one, and topping the first chart was "Ac-Cent-Tchu-Ate the Positive".
In November 1955, a composite standing chart that combined retail sales, jukebox and disk jockeys play charts but counted individual record separately was created as "The Top 100" chart, with "Love Is a Many-Splendored Thing" by The Four Aces its first No. 1.[6] This chart is the direct predecessor to the current Hot 100 chart. The jukebox chart ceased publication after the June 17, 1957, issue, the disk jockey chart after July 28, 1958, the best-seller chart after October 13, 1958.[13] After July 28, 1958, the composite chart the "Top 100" chart was also discontinued;[14] and the "Hot 100" began the following week on August 4, 1958, listing "Poor Little Fool" by Ricky Nelson as its first No. 1.[15][16] The Hot 100 currently combines singles sales, radio airplay, digital downloads, and streaming activity (including data from YouTube and other video sites). Many Billboard charts use this basic formula apart from charts dedicated to the three data sources: sales (both physical and digital), airplay and streaming.[17]
In the early period, the issue dates and the chart dates given in Billboard were different until January 13, 1962, when the issue dates and the chart dates both referred to the week ending dates.[10] The Honor Roll of Hits chart was discontinued after November 16, 1963.[13]
Billboard also publishes various music genre charts. "Harlem Hit Parade" was created in 1943 which became "Best-Selling Race Records" in 1948 and "Best-selling Rhythm & Blues Records" in 1949, and then "Soul Singles" in 1969 (currently Hot R&B/Hip-Hop Songs). "Best-selling Folk Records" was published in 1948, and this morphed into "Best-Selling Country & Western Records" in 1949, "Best-Selling C&W Records" in 1956 and "Hot Country Singles" in 1963 (now Hot Country Songs). MOR charts has been published since 1961, variously called "Easy Listening", "Middle-Road Singles" and "Pop-Standard Singles" and now Adult Contemporary.[6]Billboard charts now cover these music genres: rock, pop, country, dance, bluegrass, jazz, classical, R&B, rap, electronic, Latin, Christian, world and holiday music, and even ringtones for mobile (cell) phones.
An album chart, the "Best Selling Popular Record Albums", was first published on March 24, 1945, with The King Cole Trio its first No. 1.[18] The first chart had 10 albums, before reducing to five in the following weeks, before increasing again to 10 in 1948. The album chart was split into 33-8 and 45 rpm lists in 1950 before they recombined in 1954, then divided into mono and stereo classifications in 1959 before they merged into a 150-item pop album chart in 1963. It was eventually expanded into a 200 album list on May 13, 1967.[6] Various genre album charts were also published: Country LP chart in January 1964, R&B chart in 1965, jazz in 1969, Latin in 1973, Gospel 1974,[6] and Rock in 1981. Other charts include Classical albums, Comedy Albums, Holiday Albums, Soundtracks, Independent Albums, Catalog Album and many others besides.
At the end of each year, Billboard tallies the results of all of its charts, and the results are published in a year-end issue and heard on year-end editions of its American Top 40 and American Country Countdown radio broadcasts.[19] The first such annual charts released were for the year 1946, published on the January 4, 1947, issue,[20] although annual listing of songs had been published some years prior,[21] such as the undifferentiated annual chart based on "Honor Roll of Hits" for 1945.[22] Between 1991 and 2006, the top single/album/artist(s) in each of those charts was/were awarded in the form of the annual Billboard Music Awards, which were held in December until the awards went dormant in 2007. The awards returned in May 2011.[23]
Chart compilation methodology
For many years, a song had to be commercially available as a single to be considered for any of the Billboard charts. At the time, instead of using Nielsen SoundScan or Nielsen Broadcast Data Systems (BDS), Billboard obtained its data from manual reports filled out by radio stations and stores. For different musical genres, which stations and stores are used separates the charts; each musical genre has a core audience or retail group. Each genre's department at Billboard is headed up by a chart manager, who makes these determinations.[citation needed] According to the 100th-anniversary issue of Billboard, prior to the official implementation of SoundScan tracking in November 1991, many radio stations and retail stores removed songs from their manual reports after the associated record labels stopped promoting a particular single. Thus, songs fell quickly after peaking and had shorter chart lives. In 1990, the country singles chart was the first chart to use SoundScan and BDS.[24] They were followed by the Hot 100 and the R&B chart in 1991.[25] Today, all of the Billboard charts use this technology.[citation needed]
Before September 1995, singles were allowed to chart in the week they first went on sale based on airplay points alone. The policy was changed in September 1995, to only allow a single to debut after a full week of sales on combined sales and airplay points. This allowed several tracks to debut at number one.[citation needed]
In December 1998, the policy was further modified to allow tracks to chart on the basis of airplay alone without a commercial release. This change was made to reflect the changing realities of the music business. Previous to this, several substantial radio and MTV hits had not appeared on the Billboard chart at all, because many major labels chose not to release them as standalone singles, hoping their unavailability would spur greater album sales. Not offering a popular song to the public as a single was unheard of before the 1970s. The genres that suffered most at the time were those that increasingly impacted pop culture, including new genres such as trip hop and grunge. Among the many pre-1999 songs that had ended up in this Hot 100 limbo were The Cardigans' "Lovefool", Natalie Imbruglia's "Torn" (which peaked at 42), Goo Goo Dolls' "Iris" (which hit number 9), OMC's "How Bizarre", Sugar Ray's "Fly", and No Doubt's "Don't Speak".[citation needed]
On June 25, 2015, Billboard made changes in its chart requirements. The official street date for all new album releases was moved from Tuesday to Friday in the United States. For all sales-based charts (ranking both albums and tracks), Billboard and Nielsen changed the chart reporting period to cover the first seven days of an album's release. As a result of the changes, The Billboard 200, top albums sales, genre-based albums, digital songs, genre-based downloads, streaming songs, and genre-focused streaming surveys ran on a Friday-to-Thursday cycle. Radio Songs, which informs the Hot 100, synced to the Monday-to-Sunday period after formerly covering Wednesday to Tuesday. All other radio charts and genre tallies followed the Monday-to-Sunday cycle. The move was made to coincide with the IFPI's move to have all singles and albums released globally on Fridays.[5]
Incorporation of digital platforms
Starting on February 12, 2005, Billboard changed its methodology to include paid digital downloads from digital music retailers such as Rhapsody, AmazonMP3, and iTunes. With this policy change, a song could chart based on digital downloads alone.[26]
On July 31, 2007, Billboard changed its methodology for the Hot 100 chart to include digital streams, which at the time was obtained from Yahoo and AOL's streaming platforms. This change was made exclusively to the Billboard Hot 100 chart. The effect of this chart change was minuscule at the time because it was estimated to account for 5% of the chart's total points.[27]
In October 2012, Billboard significantly changed the methodology for its country, rock, Latin, and rap charts, when it incorporated sales of digital downloads and streaming plays into what had previously been airplay-only charts. Another change was that rather than measuring airplay only from radio stations of a particular genre, the new methodology measures airplay from all radio formats.[28] This methodology was extended to their Christian and gospel charts in late 2013.[29] These methodology changes resulted in higher positions on the genre charts for songs with crossover appeal to other genres and radio formats (especially pop) at the expense of songs that appeal almost exclusively to core fans of the given genre, a change that proved controversial with those devotees.[30]
On February 20, 2013, Billboard announced another change in the methodology for its charts that incorporated YouTube video streaming data into the determination of ranking positions on streaming charts. The incorporation of YouTube streaming data enhanced a formula that includes on-demand audio streaming and online radio streaming. The YouTube video streams that used in this methodology are official video streams, Vevo on YouTube streams, and user-generated clips that use authorized audio. Billboard said this change was made to further reflect the divergent platforms of music consumption in today's world.[31]
Continuous airplay, single sales, digital downloads, online streaming
50
A chart which uses the same methodology as the Hot 100, which tracks the top dance/electronic songs based on monitored airplay, single sales, digital downloads and monitored online streaming.
The songs will be used to determine eligibility for entry into the Hot 100.
Criteria will be based on the song's tempo.
Remixed versions of pop, rock, R&B, hip-hop and/or songs of other genres are ineligible for this chart.
Continuous airplay (Spins from exclusive reporters) Mix show airplay (Spins from Mainstream and Rhythmic stations)
40
Originally called Hot Dance Airplay when it was launched in 2003. A monitored dance music radio chart of 6 dance stations that came about as a result of the small but influential impact of dance music on the radio and the stations that program it.
Renamed Dance/Mix Show Airplay chart on November 19, 2011. The chart now includes the 157 Mainstream Top 40 and 67 Rhythmic Top 40 reporters that features mix shows in their programming.
Expanded to 40 positions, effective with the December 6, 2014 issue.
A chart that tracks the digital download sales of dance/electronic music singles, including tracks that are exclusively available online only. This chart also includes previously released dance and disco songs that became available for downloading.
Dance/Electronic Streaming Songs
streaming
25
A chart that tracks the week's top Dance/Electronic streamed radio songs and on-demand songs and videos on leading online music services.
Annual survey runs for 5–6 weeks beginning early December.
Internet charts
Chart title
Number of positions
Description
Social 50
50
A ranking of the most active artists on the world's leading social networking sites. Artists' popularity is determined by a formula blending their weekly additions of friends/fans/followers along with artist page views and weekly song plays, as measured by Next Big Sound.
Ranks the top fifty Spanish-language singles in the American music market. It was established as an airplay-only chart by Billboard in 1986. As of October 11, 2012, the chart is based on airplay across all formats, digital downloads, and streaming of Latin songs. Only predominately Spanish-language songs are eligible to rank on the chart.
Latin Airplay
Airplay (spins)
50
Ranks the most played songs on Latin radio stations in the United States and Puerto Rico regardless of genre or language.
Latin Digital Song Sales
Digital sales
50
Ranks the best-selling Spanish-language from digital music retailers as compiled by Nielsen SoundScan.
Ranks the most-listened to Spanish-language pop songs on Latin music radio stations. It was established in 1994, initially measuring airplay of songs being played on Latin pop radio stations.
Ranks the most performed song on Regional Mexican radio stations in the United States. It includes musical styles originating from Mexico as well as the Mexican-American community in the US such as Tejano. This chart is based on airplay from 65 regional Mexican radio stations compiled using information tracked by from BDS. It was established in 1994.
Ranks the most-listened to Spanish-language tropical music songs on 140 Latin music radio stations. It was established by the magazine in 1994, initially measuring airplay of songs played by a small panel of tropical music radio stations.
Ranks the most-listened to Spanish-language Latin rhythm songs. Latin rhythm is a music radio format that includes Spanish-language urban genres such as Latin hip hop and reggaeton. Established in 2005, it initially measured airplay of songs being played on 15 Latin rhythm radio stations.
Latin Streaming Songs
Streaming
Ranks play of Spanish-language streamed radio songs and on-demand songs and music videos on leading online music services.
Ranks the most popular by combining airplay from all formats of radio stations, digital download sales, streaming data and YouTube views of R&B and hip-hop songs.
Measures airplay spins on 72 rhythmic stations. Rhythmic is a music radio format that includes of a mix of dance, upbeat rhythmic pop, hip hop and R&B hits. These stations also contribute to the Dance/Mix Show Airplay panel.
Ranks the top 25 hip-hop/rap songs by combining airplay from all formats of radio stations, digital download sales, streaming data and YouTube views of rap songs.
Rap Airplay
airplay (spins)
25
Ranks the top 25 hip-hop/rap songs by airplay spins from R&B/hip-hop and rhythmic radio stations. Component of Hot Rap Songs chart.
Rap Digital Song Sales
digital sales
Top-downloaded rap songs, ranked by sales data as compiled by Nielsen SoundScan. Component of Hot Rap Songs chart.
Rap Streaming Songs
streaming
Top-streamed rap songs, ranked by sales data as compiled by Nielsen SoundScan. Component of Hot Rap Songs chart.
Hot R&B/Hip-Hop Recurrents
airplay (spins)
20
Ranks songs that have fallen below No. 50 on Hot R&B/Hip-Hop Songs and have been on that chart for over 20 weeks.
Hot R&B/Hip-Hop Recurrent Airplay
airplay (spins)
20
Ranks the songs that have fallen below No. 25 on the Hot R&B/Hip-Hop Airplay chart and have been on that chart for over 20 weeks.
Ranks the top 25 R&B songs by combining airplay from all formats of radio stations, digital download sales, streaming data and YouTube views of R&B songs.
R&B Digital Song Sales
digital sales
Top-downloaded R&B songs, ranked by sales data as compiled by Nielsen SoundScan. Component of Hot R&B Songs chart.
R&B Streaming Songs
streaming
Top-streamed R&B songs, ranked by sales data as compiled by Nielsen SoundScan. Component of Hot R&B Songs chart.
Top-downloaded songs classified as alternative (or a combination of alternative and another genre), ranked by sales data as compiled by Nielsen SoundScan.
Alternative Streaming Songs
streaming
25
Top-streamed songs classified as alternative, ranked by sales data as compiled by Nielsen SoundScan.
Ranks top R&B albums by sales as compiled by Nielsen Music. Albums must be less than 18 months old, or if older than 18 months then they must reside on the Billboard 200's top 100.[36]
Reggae Albums
10
Tastemakers
Ranked albums based on "an influential panel of indie stores and small regional chains."[37]
In December 2010, Billboard announced a new chart titled Social 50, which ranks the most active artists on the world's leading social networking sites. The Social 50 chart tallies artists' popularity using their weekly additions of friends/fans/followers, along with weekly artist page views and weekly song plays on Myspace, YouTube, Facebook, Twitter and iLike.[45]
In January 2011, Billboard introduced another chart called Uncharted, which lists new and developing artists, who are yet to appear on any major Billboard chart, "...regardless of their country of origin."[46] The ranking is based on the views and fans on social networking websites like Myspace and Facebook. It has since been discontinued.[citation needed]
In May 2014, after the Korea K-Pop Hot 100 chart was discontinued in the U.S., the Billboard K-Town column continued to provide chart information for K-pop artists on all Billboard charts.[47][48]
In June 2019, Billboard launched the Top Songwriters Chart and the Top Producers Chart, based on weekly activity on the Hot 100 and other "Hot" genre charts.[49]
In October 2021, Billboard launched the Hot Trending Songs charts, utilising real-time music-related trends and conversations on Twitter.[50]
Hakanen, Ernest (1998). "Counting Down to the Number One:Evolution of the Meaning of Popular Music Charts". Popular Music. 17 (1): 98–111. doi:10.1017/s0261143000000507. S2CID194061996.
The Billboard Hot 100 is the music industry standard record chart in the United States for songs, published weekly by Billboard magazine. Chart rankings are based on sales, online streaming, and radio play in the U.S.
A record chart, in the music industry, also called a music chart, is a ranking of recorded music according to certain criteria during a given period. Many different criteria are used in worldwide charts, often in combination. These include record sales, the amount of radio airplay, the number of downloads, and the amount of streaming activity.
Country pop is a fusion genre of country music and pop music that was developed by members of the country genre out of a desire to reach a larger, mainstream audience. Country pop music blends genres like rock, pop, and country, continuing similar efforts that began in the late 1950s, known originally as the Nashville sound and later on as Countrypolitan. By the mid-1970s, many country artists were transitioning to the pop-country sound, which led to some records charting high on the mainstream top 40 and the Billboard country chart. In turn, many pop and easy listening artists crossed over to country charts during this time. After declining in popularity during the neotraditional movement of the 1980s, country pop had a comeback in the 1990s with a sound that drew more heavily on pop rock and adult contemporary. In the 2010s, country pop metamorphisized again with the addition of hip-hop beats and rap-style phrasing.
Hot Country Songs is a chart published weekly by Billboard magazine in the United States.
"Hips Don't Lie" is a song by Colombian singer-songwriter Shakira featuring Haitian rapper Wyclef Jean, released by Epic Records in 2006 as the second single from Shakira's seventh studio album, Oral Fixation, Vol. 2 (2005). Shakira and Jean wrote the lyrics and jointly composed the music with additional co-writing by Shakira's percussionist Archie Pena. The song was produced by Shakira and Jean with additional co-production by Jerry Duplessis. "Hips Don't Lie" is a reworking of Jean's earlier single "Dance Like This", therefore it features additional composing credits by Omar Alfanno, Duplessis, Luis Días, and LaTavia Parker. The song incorporates samples from "Amores Como el Nuestro" written by Alfanno, and "Carnaval " written by Días.
Billboard Year-End charts are cumulative rankings of entries in Billboard magazine charts in the United States in any given chart year. Several hundred Year-End charts are now published by Billboard, the most important of which are the single or album charts based on Hot 100 and Billboard 200 respectively.
The Billboard Hot Latin Songs is a record chart in the United States for Latin songs, published weekly by Billboard magazine. Since October 2012, chart rankings are based on digital sales, radio airplay, and online streaming, and only predominantly Spanish-language songs are allowed to rank. The chart was established by the magazine on September 6, 1986, and was originally based on airplay on Latin music radio stations. Although the chart predominantly allows Spanish-language songs, songs in English and Portuguese have charted.
American country music singer Carrie Underwood has released nine studio albums, one greatest hits album, and 29 singles. Underwood rose to fame after winning the fourth season of American Idol in 2005. Her debut album, Some Hearts, was released in 2005 and is the fastest-selling debut country album in Nielsen SoundScan history. It also became the best-selling solo female country debut in Recording Industry Association of America (RIAA) history, as well as the top-selling debut album of any American Idol contestant in the United States.
Hitlisten, also known as Tracklisten, is a Danish top 40 record chart that is updated every Wednesday at midnight on the website hitlisten.nu. The weekly Danish singles chart combines the 40 best-selling tracks from streaming and legal music downloads. The Danish albums chart combines downloads, streaming and also sales of CDs. There is a separate vinyl chart. The data is collected by Nielsen Music Control, who also compile the chart on behalf of IFPI.
English singer-songwriter Adele has released four studio albums, one video album, two extended plays, 17 singles and eleven music videos. Adele has sold over 70 million in pure album sales and over 100 million in album equivalent units worldwide over four studio albums and one video album as of December 2021. She was named the best-selling album artist of the 2010s decade in the US and worldwide. She has also sold over 100 million in single sales with total sales records over 170 million as of December 2021. She also became the best-selling female artist of the 21st century in the UK. Her album 21 became the best-selling album of the 21st century.
"I Gotta Feeling" is a song by American group the Black Eyed Peas from their fifth studio album The E.N.D. (2009). It was written by the group members with the song's producers David Guetta and Frédéric Riesterer. The song was released as the second single from The E.N.D. on June 15, 2009, by Interscope Records.
Prince released several hundred songs both under his own name and under pseudonyms and/or pen names, as well as writing songs which have been recorded by other artists. Estimates of the actual number of songs written by Prince range anywhere from 500 to well over 1,000. He has released 117 singles, 41 promotional singles, 24 internet singles, and eight internet downloads.
"Cruise" is a song recorded by American country music duo Florida Georgia Line. It was first released to iTunes in April 2012 and then to radio on August 6, 2012 as the first single from their extended play It'z Just What We Do. It was written by group members Brian Kelley and Tyler Hubbard with Joey Moi, Chase Rice, and Jesse Rice. It is included on their first album for Republic Nashville, Here's to the Good Times, released on December 4. "Cruise" is the best-selling country digital song of all time in the United States as of January 2014. The song is considered the foremost example of the genre of country music termed "bro-country".
"Let Her Go" is a song recorded by English singer-songwriter Passenger. It was recorded at Sydney's Linear Recording and co-produced by Mike Rosenberg and Chris Vallejo. The recording features Australian musicians Stu Larsen, Georgia Mooney, Stu Hunter, Cameron Undy, and Glenn Wilson. "Let Her Go" was released on 24 July 2012 as the second single from Passenger's fourth album, All the Little Lights.
"Counting Stars" is a song by American pop rock band OneRepublic from their third studio album, Native (2013). The song was written by lead singer Ryan Tedder, and produced by Tedder and Noel Zancanella. It was released as the album's second single on June 14, 2013.
"Happy" is a song written, produced, and performed by American musician Pharrell Williams, released as the only single from the soundtrack album for the film Despicable Me 2 (2013). The song was first released on November 21, 2013, alongside a long-form music video. The song was reissued on December 16, 2013, by Back Lot Music under exclusive license to Columbia Records, a division of Sony Music. The song also served as the lead single from Williams's second studio album, Girl (2014).
"See You Again" is a song by American rapper and singer Wiz Khalifa featuring fellow American singer-songwriter Charlie Puth. It was commissioned for the soundtrack of the 2015 film Furious 7 as a tribute to Fast & Furious actor Paul Walker, who died in a single-vehicle crash on November 30, 2013. The song was released on March 10, 2015, as the soundtrack's lead single in the United States. It was later included as a bonus track on the international release of Puth's debut album, Nine Track Mind.
"Hello" is a song recorded by English singer-songwriter Adele, released on 23 October 2015 by XL Recordings as the lead single from her third studio album, 25 (2015). Written by Adele and the album's producer, Greg Kurstin, "Hello" is a piano ballad with soul influences, and lyrics that discuss themes of nostalgia and regret. Upon release, the song garnered critical acclaim, with reviewers comparing it favourably to Adele's previous works and praised its lyrics, production and Adele's vocal performance. It was recorded in Metropolis Studios, London.
"Shape of You" is a song by English singer-songwriter Ed Sheeran. It was released on 6 January 2017 as one of the double lead singles from his third studio album ÷ (2017), along with "Castle on the Hill". The dancehall and R&B-infused pop song was written by Sheeran, Steve Mac and Johnny McDaid. Due to its interpolation of "No Scrubs" by TLC, Kandi Burruss, Tameka "Tiny" Cottle, and Kevin "She'kspere" Briggs are also credited as writers. The song was produced by Sheeran and Mac.
"Save Your Tears" is a song by Canadian singer the Weeknd from his fourth studio album, After Hours (2020). It was released as the album's fourth and final single on August 9, 2020 in Europe and November 24, 2020 in the US. The Weeknd wrote and produced the song with Max Martin and Oscar Holter with Belly and DaHeala receiving additional writing credits. The record was met with universal acclaim with praise for the production and the Weeknd's vocals.
↑ "Billboard R&B Albums". Billboard. Archived from the original on December 17, 2015. Retrieved December 16, 2015. Description per "How it works" section of webpage.
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