SONIC4D Contact force or pressure increases the size of the a-spot which decreases the constriction resistance and the electrical contact resistance. Each contact is a piece of electrically conductive material, typically metal. Form A contacts ("make contacts") are normally open contacts. In most cases, the rule is break-before-make or B-B-M; that is, the NO and NC contacts are never simultaneously closed during the transition between states. Hayden, New York, 1966; large parts of the 5th edition are on line here Archived 2017-07-05 at the Wayback Machine. Its operation is logically inverted from Form A. An alternate notation for Form B is SPST-NC.|Many Computers had Controls