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The stated level all depths are measured from.
Also known as: Sounding datum notation, Depth datum chart, Lowest astronomical tide datum
On a nautical chart the chart datum is the level below which depths are measured and above which drying heights are given, stated in the chart's title block.
Names the level from which all soundings and drying heights on the chart are measured.
Contexts: Navigation
Is chosen so the tide will rarely fall below it, which means real depths are usually greater than charted and the chart errs towards safety.
Contexts: Navigation
A block of printed letters in the chart's title panel naming the level, beside a diagram of stacked horizontal lines relating it to the other tidal levels.