page_title: Rotary dial
section_title: Construction
hierarchical_section_title: Rotary dial / Construction
caption_attribution_description: Ericssons Bakelittelefon 1931
context_page_description: A rotary dial is a component of a telephone or a telephone switchboard that implements a signaling technology in telecommunications known as pulse dialing. It is used when initiating a telephone call to transmit the destination telephone number to a telephone exchange.
  On the rotary phone dial, the digits are arranged in a circular layout so that a finger wheel may be rotated against spring tension with one finger. Starting from the position of each digit and rotating to the fixed finger stop position, the angle through which the dial is rotated corresponds to the desired digit. Compact telephones with the dial in the handset had all holes equally spaced in the dial, and a spring-loaded finger stop with limited travel.
  When released at the finger stop, the wheel returns to its home position driven by the spring at a speed regulated by a centrifugal governor device. During this return rotation, the dial interrupts the direct electrical current of the telephone line the specific number of times associated with each digit and thereby generates electrical pulses which the telephone exchange decodes into each dialed digit.
context_section_description: A rotary dial typically features a circular construction. The shaft that actuates the mechanical switching mechanism is driven by the finger wheel, a disk that has ten finger holes aligned close to the circumference. The finger wheel may be transparent or opaque permitting the viewing of the face plate, or number plate below, either in whole, or only showing the number assignment for each finger hole. The faceplate is printed with numbers, and sometimes letters, corresponding to each finger hole. The 1 is normally set at approximately 60 degrees clockwise from the uppermost point of the dial, or approximately at the 2 o'clock position, and then the numbers progress counterclockwise, with the 0 being at about 5 o'clock. A curved device called a finger stop sits above the dial at approximately the 4 o'clock position. The physical nature of the dialing mechanism on rotary phones allowed the use of physical locking mechanisms to prevent unauthorized use. The lock could be integral to the phone itself or a separate device inserted through the finger hole nearest the finger stop to prevent the dial from rotating.
caption: A 1931 Ericsson rotary dial telephone without lettering on the finger wheel, typical of European telephones. The 0 precedes 1.