Talk:Ordnance datum

Maps Stub‑class

	This article is within the scope of WikiProject Maps, a collaborative effort to improve the coverage of Maps and Cartography on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.MapsWikipedia:WikiProject MapsTemplate:WikiProject MapsMaps
Stub	This article has been rated as Stub-class on Wikipedia's content assessment scale.
???	This article has not yet received a rating on the project's importance scale.
	This article has been automatically rated by a bot or other tool as Stub-class because it uses a stub template. Please ensure the assessment is correct before removing the `\|auto=` parameter.

Tides

If Ordnance Datum was 'Mean Sea Level', then low tides should usually be expressed as negative vaues. They are not on tide timetables. So OD must refer to Low Spring Tide level.88.108.30.110 20:11, 12 November 2006 (UTC)[reply]

Tide tables are expressed relative to Chart Datum, not Ordnance Datum. Chart Datum is indeed based on Lowest Astronomical Tide UKHO FAQ. jnestorius^(talk) 21:23, 12 November 2006 (UTC)[reply]

Spelling

I notice that the spelling of Portmore is given here as Portmoor. http://www.geograph.org.uk/photo/5094244 gives the version I am more familiar with. Is Portmoor an error, or an acceptable alternative?