Editing Fourteen-segment display (section)

===Incandescent lamp===
Multiple segment alphanumeric displays are nearly as old as the use of electricity. A 1908 textbook <ref>I. C. S. Reference Library Volume 4B, Scranton, [[International Textbook Company]], 1908, no ISBN</ref> describes an alphanumeric display system using incandescent lamps and a mechanical switching arrangement. Each of 21 lamps was connected to a switch operated by a set of slotted bars, installed in a rotating drum.  This ''commutator'' assembly could be arranged so that as the drum was rotated, different sets of switches were closed and different letters and figures could be displayed.  The scheme would have been used for "talking" signs to spell out messages, but a complete set of commutator switches, drums and lamps would have been required for each letter of a message, making the resulting sign quite expensive.