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A projection clock (also called ceiling clock) is an analogue or digital clock equipped with a projector that creates an enlarged image of the clock face or display on any surface usable as a projection screen, most often the ceiling. [1] The clock can be placed almost anywhere if only the projected image must be seen.
The Signaltron main departure board at Praha-Smíchov station, Czech Republic (2012), manufactured by Pragotron Schematic of a split-flap display in a digital clock display An animation of how a split-flap display works Flap departure board at Gare du Nord, Paris (2007) Section of a split-flap display board at Frankfurt (Main) Hauptbahnhof (2005) Enlarged inner workings of a split-flap clock
Some clocks, usually digital ones, include an optical projector that shines a magnified image of the time display onto a screen or onto a surface such as an indoor ceiling or wall. The digits are large enough to be easily read, without using glasses, by persons with moderately imperfect vision, so the clocks are convenient for use in their ...
Standard-quality 32 768 Hz resonators of this type are warranted to have a long-term accuracy of about six parts per million (0.0006%) at 31 °C (87.8 °F): that is, a typical quartz clock or wristwatch will gain or lose 15 seconds per 30 days (within a normal temperature range of 5 to 35 °C or 41 to 95 °F) or less than a half second clock ...
Digital clocks typically use the 50 or 60 hertz oscillation of AC power or a 32,768 hertz crystal oscillator as in a quartz clock to keep time. Most digital clocks display the hour of the day in 24-hour format; in the United States and a few other countries, a commonly used hour sequence option is 12-hour format (with some indication of AM or PM).
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