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  2. History of timekeeping devices - Wikipedia

    en.wikipedia.org/wiki/History_of_timekeeping_devices

    The English word clock first appeared in Middle English as clok, cloke, or clokke. The origin of the word is not known for certain; it may be a borrowing from French or Dutch, and can perhaps be traced to the post-classical Latin clocca ('bell'). 7th century Irish and 9th century Germanic sources recorded clock as meaning 'bell'. [74]

  3. Doomsday Clock - Wikipedia

    en.wikipedia.org/wiki/Doomsday_Clock

    The Doomsday Clock is a symbol that represents the likelihood of a human-made global catastrophe, in the opinion of the members of the Bulletin of the Atomic Scientists. [1] Maintained since 1947, the Clock is a metaphor, not a prediction, for threats to humanity from unchecked scientific and technological advances.

  4. Atmos clock - Wikipedia

    en.wikipedia.org/wiki/Atmos_clock

    Atmos clock. Jaeger-LeCoultre's Atmos clock on display. Atmos is the brand name of a mechanical torsion pendulum clock manufactured by Jaeger-LeCoultre in Switzerland which does not need to be wound manually. It gets the energy it needs to run from temperature and atmospheric pressure changes in the environment, and can run for years without ...

  5. Clock - Wikipedia

    en.wikipedia.org/wiki/Clock

    Casio F-91W digital watch, a historically popular watch. A clock or chronometer is a device that measures and displays time. The clock is one of the oldest human inventions, meeting the need to measure intervals of time shorter than the natural units such as the day, the lunar month, and the year. Devices operating on several physical processes ...

  6. Atomic clock - Wikipedia

    en.wikipedia.org/wiki/Atomic_clock

    The SI second is defined as a certain number of unperturbed ground-state hyperfine transitions of the caesium-133 atom. Caesium standards are therefore regarded as primary time and frequency standards. Caesium clocks include the NIST-F1 clock, developed in 1999, and the NIST-F2 clock, developed in 2013. [42] [43]

  7. Caesium standard - Wikipedia

    en.wikipedia.org/wiki/Caesium_standard

    A caesium atomic fountain used as part of an atomic clock. The caesium standard is a primary frequency standard in which the photon absorption by transitions between the two hyperfine ground states of caesium-133 atoms is used to control the output frequency. The first caesium clock was built by Louis Essen in 1955 at the National Physical ...

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  9. Hourglass - Wikipedia

    en.wikipedia.org/wiki/Hourglass

    An hourglass (or sandglass, sand timer, or sand clock) is a device used to measure the passage of time. It comprises two glass bulbs connected vertically by a narrow neck that allows a regulated flow of a substance (historically sand ) from the upper bulb to the lower one due to gravity .

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