Music is art. But its success is measured in very commercial terms – how many records were sold. Sales figures translate to top 40 chart position.

There are other measures of a song’s success. How fast it went up – and down – the charts. And we also consider how long a song or album stayed on the charts.

There are some epic results, especially on the album charts. A Johnny Mathis best of in 1958 stayed on the album charts for 490 weeks. Dark Side of the Moon did 15 years, and still gets back on the charts every now and then. And Rumours, by Fleetwood Mac, has 926 weeks on the UK album charts.