Pushwheel switches are operated by a rotating wheel or dual buttons and are activated by a rotating shaft with several stop positions. They are made of thermoplastic or metallic materials and are available in standard, miniature and subminiature sizes. Some pushwheel switches are mounted on printed circuit boards (PCBs) in order to control the behavior of electronic devices. Changing the position of the rotating shaft generates a circuit code in binary, octal, or hexadecimal format. Binary coded decimal (BCD) circuit codes represent each decimal digit with a four-bit binary number. Octal systems represent quantities with eight digits: 0, 1, 2, 3, 4, 5, 6 and 7. Hexadecimal systems represent quantities with 16 symbols: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E and F. Binary, octal, and hexadecimal complements are also available. Some pushwheel switches use Gray code, a non-arithmetic circuit code that does not assign specific weights to bit positions.