How do songs get into The Top 40?
The chart is based on how many tracks are bought over the counter, or downloaded from legal websites.
The sales figures come from over 5,600 shops including all the major high street chains as well as 600 independent stores. Downloads are counted from major websites like iTunes and Napster but The Top 40 also includes sales of tracks bought from smaller specialist websites. .
Each week the sales information is added together, this happens after the shops close on Saturday. The calculations are completed by noon the next day to produce the official weekly charts.