Fares for Caltrain service are based on the number of zones traveled, which is considered to be the number of zones "touched" between the origin and destination. For instance, a passenger that boards at a Zone 1 station and departs at a Zone 1 station is considered to travel within one zone. A passenger that boards at a Zone 2 station and departs at a Zone 4 station is considered to travel within three zones (Zones 2, 3, and 4). When purchasing a ticket from the station ticket machine, the machine assumes the origin zone is the same as the station's zone, and prompts the passenger to select a destination zone, but the origin zone can be changed if necessary.