Chart Navigation & Plotting · Chart Symbols
On a nautical chart, a sounding shown as an underlined figure (e.g., an underlined 'rock') generally indicates:
- AA measured depth of clear water
- BA drying height — a feature that uncovers at low water, measured above the sounding datum✓ Correct
- CA radar conspicuous object
- DA magnetic anomaly
Explanation
An underlined figure denotes a drying height — the feature uncovers at chart datum and the figure gives its height above MLLW. Plain soundings give depth below datum. Chart No. 1 is the key to all such symbols and abbreviations.
Authority: U.S. Chart No. 1
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