For the purposes of calculating sales, a single is currently defined by the Official Charts Company (OCC) as either a 'single bundle' having no more than four tracks and not lasting longer than 25 minutes or one digital audio track not longer than 15 minutes with a minimum sale price of 40 pence. The rules have changed many times as technology has developed, the most notable being the inclusion of digital downloads in 2004 and streaming in 2014. The highest-selling single by a solo female artist is "Believe" by Cher – released in October 1998, it has sold over 2.4 million copies in the UK.