DUNITS


  1. metres: depths are specified in metres (SI units of length).
  2. fathoms and feet: depths are specified in fathoms (units of six feet of depth) and feet.
  3. feet: depths are specified in feet (imperial units of length).
  4. fathoms and fractions: depths are specified in fathoms (units of six feet of depth) and fractions of fathoms.