Binary or two-valued means that a system can assume one of two possible states in each case, e.g. yes/no, current/no current, zero/one, high/low. This bivalence forms the basis for binary digital signals, their calculation and processing. Every value can be expressed by bivalence, as well as digits, characters and letters. The unit for bivalence is the binary digit(bit), which forms the basis for the binary system and the dual system. If a system works with three valences, it is trinary or ternary.