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  2. Unit of time - Wikipedia

    en.wikipedia.org/wiki/Unit_of_time

    A unit of time is any particular time interval, used as a standard way of measuring or expressing duration. The base unit of time in the International System of Units (SI), and by extension most of the Western world, is the second, defined as about 9 billion oscillations of the caesium atom. The exact modern SI definition is " [The second] is ...

  3. Metric time - Wikipedia

    en.wikipedia.org/wiki/Metric_time

    t. e. Metric time is the measure of time intervals using the metric system. The modern SI system defines the second as the base unit of time, and forms multiples and submultiples with metric prefixes such as kiloseconds and milliseconds. Other units of time – minute, hour, and day – are accepted for use with SI, but are not part of it.

  4. History of timekeeping devices - Wikipedia

    en.wikipedia.org/wiki/History_of_timekeeping_devices

    The idea of using atomic transitions to measure time was first suggested by the British scientist Lord Kelvin in 1879, [204] although it was only in the 1930s with the development of magnetic resonance that there was a practical method for measuring time in this way. [205] A prototype ammonia maser device was built in 1948 at NIST. Although ...

  5. International System of Units - Wikipedia

    en.wikipedia.org/wiki/International_System_of_Units

    mole. amount of substance. cd. candela. luminous intensity. The SI comprises a coherent system of units of measurement starting with seven base units, which are the second (symbol s, the unit of time), metre (m, length), kilogram (kg, mass), ampere (A, electric current), kelvin (K, thermodynamic temperature), mole (mol, amount of substance ...

  6. History of timekeeping devices in Egypt - Wikipedia

    en.wikipedia.org/wiki/History_of_timekeeping...

    Ancient Egyptian sundial (c. 1500 BC), from the Valley of the Kings, used for measuring work hour. Daytime divided into 12 parts. The ancient Egyptians were one of the first cultures to widely divide days into generally agreed-upon equal parts, using early timekeeping devices such as sundials, shadow clocks, and merkhets (plumb-lines used by early astronomers).

  7. Chronometry - Wikipedia

    en.wikipedia.org/wiki/Chronometry

    Chronometry[a] or horology[b] (lit. 'the study of time') is the science studying the measurement of time and timekeeping. [3] Chronometry enables the establishment of standard measurements of time, which have applications in a broad range of social and scientific areas. Horology usually refers specifically to the study of mechanical timekeeping ...

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