Nautical Terms...
Sounding:
A measurement of
the depth of water.
The numbers on this map indicate the
sounding in fathoms at this location.
Larger number = number of fathoms
Subscript (smaller number) = additional feet
Fathom: A unit of measure used to determine the
depth of water or objects in the water. It is equal in
length to 6 feet (1.8 m) – the approximate distance
between a man's outstretched hands.