variance-The square of the standard deviation.

variation-In nautical and aeronautical navigation, and in some localities surveying, the term variation is used instead of, and meaning, magnetic declination. The regular variations are secular, the change from year to year which usually extends for many decades in the same direction; annual, having a period of one year; and diurnal, having a daily period. The irregular variations are known, when severe, as magnetic storms. Locally the magnetic field may be affected by direct-current electricity and other artificial disturbances. It was once a common practice of surveyors to denote as variation the net amount by which the compass departed from the direction taken as north in the description of a particular line, even when this was known to be slightly at variance with the celestial meridian.

variation of coordinate method-A method of adjusting triangulation by least squares, in which a synthetic, mathematically harmonious figure is assumed to approximate closely the observed measurements and include all the previously adjusted data that must be held fixed in the adjustment.

variation of the compass-Difference between true north as determined by the Earth’s axis of rotation and magnetic north as determined by the earth’s magnetism. The variation is designated as east or positive when the magnetic needle is deflected to the east of true north, and as west or negative, when the deflection is to the west of true north; magnetic declination.

variation of the pole-A wandering of the poles of the Figure of the Earth with respect to its poles of rotation.

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Source: NSPS “Definitions of Surveying and Related Terms“, used with permission.

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