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The UK Singles Chart is the official record chart in the United Kingdom. Until 1983, it was compiled weekly by the British Market Research Bureau (BMRB) on behalf of the British record industry with a two-week break each Christmas. The BMRB used motorcycle couriers to collect the sales figures taken up to the close of trade on Saturday. This data was compiled on Monday and given to the BBC on Tuesday to be announced on Johnnie Walker's afternoon show and later published in Music Week. On 4 January 1983, the chart was taken over by Gallup who expanded the chart from the Top 75 to the Top 100 and began the introduction of computerised tills which automated the data collection process.The chart was based entirely on sales of physical singles from retail outlets and announced on Tuesday until October 1987, when the Top 40 was revealed each Sunday, due to the new automated process. During the 1980s there were a total of 191 singles which took the UK chart number 1 spot.In terms of number-one singles, Madonna was the most successful single act of the decade, as six of her singles reached the top spot.George Michael had significant involvement with seven number-one singles; with two number-one singles as a solo artist, four as a member of pop duo Wham!, and one as a duet with Aretha Franklin. The longest duration of a single at number one was nine weeks, achieved by Frankie Goes to Hollywood's "Two Tribes" in 1984.The best-selling single of the decade was "Do They Know It's Christmas?" by Band Aid, selling over 3.5 million copies, and passing "Mull of Kintyre" by Wings' to become the best-selling single ever. "Do They Know It's Christmas?" is currently the second best-selling song after "Candle in the Wind 1997" by Elton John.]The 1980s saw the introduction of the cassette single or "cassingle") alongside the 7-inch and 12-inch record formats and in 1987 major record labels developed a common format for the Compact Disc single. For the chart week ending 3 May 1989, chart regulations confined Kylie Minogue's song "Hand on Your Heart" to number two. Minogue would have reached number one if sales from cassette singles were included but they were sold for £1.99 – cheaper than was allowed at the time. Following the debacle the British Phonographic Industry reduced the minimum price for cassette singles to become eligible towards sales figures