Precision Timing

Word list
UTC Time
      Coordinated Universal Time.
      This is a time scale based on atomic clocks,
      by definition cesium clocks.

      Bureau International des Poids et Mesure.
      The international bureau of weights and measurements, in Paris.
      Responsible of the UTC time scale.

Standard Time, (In Sweden it is named Normal time)
      The time used during the winter. This time equals UTC + n
      where n is the offset from UTC.
      In central Europe the offset is one hour (+1h) for standard time.

Daylight Saving Time
      Normally used during the summer,
      In Europe often named summer time.
      In central Europe this time is UTC + 2 hours

Local Time
      The current time used at a location.
      During the winter local time equals standard or normal time.
      During the summer local time equals Daylight Saving Time. Note
      that the offset between Local time and UTC time is not constant,
      it varies in locations where Daylight Saving Time is used.

Leap Second
      The rotation speed of the Earth is less stable than
      modern atomic clocks. Examples of time scales that are
      based on earth rotation are UT, UT1 and GMT.
      To keep the difference between UTC and earth rotation time
      scales below one second, now and then a leap second is
      inserted. (Or removed).

      Currently the earth is rotating "too slow." An extra positive
      leap second is most likely to occur "now and then."
      Now and then is not known more than half a year in advance.
      Last years they occurred between 1 and 2.5 years apart.

Modified Julian Date, MJD
      This is a linear sequence of day numbers, that equals
      the Julian Date less than 2 400 000.5 days.
      The origin of MJD equals 0000 hours UTC time, 17 November 1858.
      MJD is specified by a number with five significant figures.
      (The Julian Date has its origin at 1200 hours UTC and its value
      consequently was 2 400 000.5 at the time of MJD origin.)

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© 1995 Erland Brännström, Precision Timing, SWEDEN.