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British Dictionary definitions for ordnance datum

ordnance datum

noun
  1. mean sea level calculated from observation taken at Newlyn, Cornwall, and used as the official basis for height calculation on British mapsAbbreviation: OD
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Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012