ordnance datum

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ordnance datum

n
(Surveying) mean sea level calculated from observation taken at Newlyn, Cornwall, and used as the official basis for height calculation on British maps. Abbreviation: OD
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
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