The operation of the coherer is based on the phenomenon of electrical contact resistance. Improvements included all-wheel drive and electrical contact. The function of contact cleaner can be understood by consideration of electrical contact theory. However, only CoSi has a sufficiently low resistance to form an effective electrical contact. This micro-lifting prevents the truck wheels from making a solid electrical contact with the track. Some tubular lamps have an electrical contact at either end. The brushes make electrical contact with the rotating slip rings. The shell may serve as an electrical contact or only as a mechanical support. A separator prevents direct electrical contact between anode and cathode. They function as an ohmic electrical contact in the middle of a semiconductor device. Because the switch doesn't have an actual electrical contact, there is no debouncing necessary. The tether's far end can be left bare, making electrical contact with the ionosphere. On a Typex rotor, each electrical contact was doubled to improve reliability. They establish the electrical contact between the electronics on the card and on the motherboard.