Definition
The visible horizon lies below the true horizontal by the dip angle, approximately 1.76 times the square root of the height of eye in metres, expressed in minutes of arc. At 2.5 metres in a small yacht, dip is about 2.8 minutes; at 9 metres on a ship's bridge wing, about 5.3 minutes. Dip is always subtracted from the sextant altitude. An error of one metre in the assumed height costs a few tenths of a mile.
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