page_title: Prussian semaphore system
section_title: Indicators and their control
hierarchical_section_title: Prussian semaphore system / Construction and function / Indicators and their control
caption_attribution_description: Code used by the Prussian Optical Telegraph between Berlin and Koblenz. All arms used.
context_page_description: The Prussian Semaphore System was a telegraphic communications system used between Berlin and the Rhine Province from 1832 to 1849. It could transmit administrative and military messages by optical signal over a distance of nearly 550 kilometres. The telegraph line comprised 62 stations each furnished with a signal mast with six cable-operated arms. The stations were equipped with telescopes that operators used to copy coded messages and forward them to the next station. Three dispatch departments located in Berlin, Cologne and Koblenz handled the coding and decoding of official telegrams. Although electric telegraphy made the system obsolete for military use, simplified semaphores were still used for railway signals.
context_section_description: The moving signal arms were suspended with counterweights to enable easy adjustment.  The indicators measured 1.74 m × 0.33 m.  Only two of the original indicators still exist today; one is on display in the Boerdemuseum in Ummendorf and the other in the Museum for Communication in Berlin.  These arms, as well as preserved construction drawings, suggest that the arms consisted of a wooden framework with a wood or sheet metal interior.  This provided greater wind resistance.
  The operating mechanism of the system was located at the bottom of the mast in the observation room of the station.  The indicators were operated with six adjustable levers arranged above each other in pairs.  The position of each lever corresponded to the three-level alignment of the signal arms on the mast above.  The levers and signal arms were connected by hemp ropes and later by wire cables.  The levers each were lockable in four different positions, that exactly corresponded to the position of signal arm: 0° (arm hanging downward parallel to the mast), 45°, 90° (perpendicular to the mast), and 135°.  Each position was relative to the mast.
caption: telegraph-alphabet with German "Umlaute"
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