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За нуль глубин на английских картах принят средний уровень сизигийных малых вод, на отечественных картах - наинизший возможный уровень моря, называемый теоретическим нулем глубин - прим. ред
http://www.1yachtua.com/School/navigation5.htm

"Their" theoretical zero depth is quite different from "ours" - it's mean sea level (!) rather than lowest. Типичный "ложный друг".

"2. What is meant by "altitude above sea level" and how is the zero reference determined.
Heights above sea level, like mountains or whatever, have traditionally been defined (and still are in most cases) in terms of a measurement of 'mean sea level' at one or more locations. That mean sea level, once determined at the location, is then carried around the country by means of surveyors' spirit levelling apparatus (i.e. better versions of the levelling apparatus you must have seen surveyors use in the road or construction industry).
So, for example, here in the U.K. we define heights above sea level in terms of 'Ordnance Datum Newlyn' (ODN) which is the mean level of the sea at Newlyn in Cornwall in S.W.England in the period May 1915 to April 1921 (which replaced an earlier Ordnance Datum Liverpool based on sea level in that port in 1844). That level has been carried around the country by surveyors' methods (i.e. levelling, which is equivalent to imagining a set of ficticious thin canals with no flow permeating the country which allow the ODN level, the 'zero' reference level of the height system, to be transferred from one place to another). So, a height of a Scottish mountain, for example, means height above ODN, which is the height above the sea level at Newlyn many years ago. Similarly, NAP (Normaal Amsterdam Peil) in the Netherlands is approximate mean sea level at Amsterdam (and represented by a mark in a shopping centre). French heights are relative to mean sea level at Marseille at a particular epoch.

In many countries, like the US or India with 2 coastlines there are often two or more datums as the distance from the sea to the mountains (or whatever) can be great and errors creep into the measurements. Also for oceanographic reasons sea level can really be different in different places i.e. mean sea level is not a 'level surface' (see 1). "
http://www.pol.ac.uk/psmsl/puscience/#2


The ref might seem irrelevant, but when they say zero-level COUNTUR (!) or chart datum, they mean THIS zero

Just one another link out of very many
Properties of seawater
... in the ocean is thus from near zero (surface) to 10,000 dbar (deepest). ... In the
ocean, we commonly use the sea surface as our "reference" pressure for ...
sam.ucsd.edu/sio210/lect_2/lecture_2.html - 42k

I failed to find a single English source, where they would count from this "theoretical absolute zero"
По-моему, вывод однозначный - если и употреблять дословный перевод, то только с таким пояснением в скобках.
Варианты - "Theor. absolute zero", "zero reference" (to avoid confusion with "their" term) etc.


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Note added at 1 hr 32 mins (2004-05-29 17:36:46 GMT)
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Georgy: I agree with your point, but still feel that if just \"theoretical zero-depth\" is left in the translation, it will inevitably cause confusion among English-speaking audience (readers)

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Note added at 1 hr 56 mins (2004-05-29 18:00:20 GMT)
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Well, I still see a difference between the case of \"0F vs 0C\" (two different measurement units exlplicitly indicated) and \"theoretical zero vs theoretical zero\" (two identical terms meaning different things. I\'ve seen many pro\'s finding such cases extremely confusing.
(e.g. psi)

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Note added at 1 day 18 hrs 44 mins (2004-05-31 10:48:46 GMT)
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My unbiased :) opinion remains the same - zero depth or chart datum (doesn\'t really matter, for all I know) - it has to be wigh a qualifier (national - CD or ZD adopted/used in the USSR (Russia), or technical - lowest possible....)