Hopefully this might help people when buying tickets or using their Oyster:
http://www.bbc.co.uk/go/news/uk-england-london-13389363/ext/story-body/www.cs.ucl.ac.uk/-/http://www.cs.ucl.ac.uk/staff/n.lathia/files/fares_graph.jpg
Also a news article related to it:
http://www.bbc.co.uk/news/uk-england-london-13389363
http://www.bbc.co.uk/go/news/uk-england-london-13389363/ext/story-body/www.cs.ucl.ac.uk/-/http://www.cs.ucl.ac.uk/staff/n.lathia/files/fares_graph.jpg
Also a news article related to it:
http://www.bbc.co.uk/news/uk-england-london-13389363