Shenzhen Tong is a pre-paid currency card similar to Oyster Card system in London and the Octopus card system used in Hong Kong. The multiple fare card stores credit purchased at stations. The card can be used by waving it in front of the card reader located at all entrances and exits to the subway system. Riders who pay for metro fare with a card receive a 5% discount. Since March 1, 2008, riders who pay for a bus fare with a card and then a subway fare within 90 minutes receive an additional 0.4 RMB discount on the subway fare. Card users pay a distance based fare.