Local mean time

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The equation of time — above the axis a sundial will appear fast relative to a clock showing local mean time, and below the axis a sundial will appear slow.

Local mean time is a form of solar time that corrects the variations of local apparent time, forming a uniform time scale at a specific longitude. Its uniformity depends only on the accuracy of the clocks used to measure it.

Local mean time was used from the early 19th century, when local solar time or sundial time was last used, until standard time was adopted on various dates in the several countries. Standard time means that the same time is used throughout some region—usually, it was either offset from Greenwich Mean Time or was the local mean time of the capital of the region. The difference between local mean time and local apparent time is the equation of time.

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