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Day Skipper - Part 4 - Depths
and heights
 All depths
on a chart are measured below chart datum (CD), and drying heights are
measured above it. This is a level derived from the lowest astronomical
tide (LAT), which is the lowest tide predicted under average meteorological
conditions. It should be noted that occasionally, tides are predicted
to fall below CD or LAT. Heights of objects on the land are measured above
'High Water', which is usually determined as mean high water springs.
Although this seems confusing, it allows an extra safety margin in case
you forget and calculate heights above CD.
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