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A correction to the sextant height to account for the height of eye (HE) at the sight time. In math terms, it is the angle between the geometric horizon (true horizontal) and the visible horizon which is tilted because of the observer's height above the water. The effect of the dip is to make every sextant height too large by a small amount (equal to 0.97' times the square root of HE in feet). Dip corrections are tabulated in the Nautical Almanac. The dip correction expressed in miles (1' = 1 mile) is approximately equal to the distance from the observer to the last visible point on the horizon.

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