A standard Oyster card is a blue credit card-sized stored value card which can hold a variety of single tickets, period tickets and travel permits which must be added to the card prior to travel. It is also a contactless smart card which passengers must touch onto an electronic reader when entering and leaving the transport system in order to validate it or deduct funds. The cards may be "recharged" in person from numerous sales points, by recurring payment authority or by online purchase. The card is designed to reduce the number of transactions at ticket offices and the number of single paper tickets sold on the London transport network. Use is encouraged by offering substantially cheaper fares on Oyster than payment with cash.