ordnance datum
noun
mean sea level calculated from observation taken at Newlyn, Cornwall, and used as the official basis for height calculation on British maps
Abbreviation: OD
Words nearby ordnance datum
ordinary-language philosophy,
ordinate,
ordination,
ordn.,
ordnance,
ordnance datum,
ordnance survey,
ordo,
ordonnance,
ordos,
ordovician