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Other factors that you should take notice of when looking at the nautical chart are:
The depths note, This shows which units of measurement are used to indicate the depths on the chart. You may read SOUNDINGS IN FATHOMS AND FEET or SOUNDINGS IN METERS.
Sounding in fathoms and feet indicates that soundings are in fathoms with subscript in feet. The larger number indicates fathoms, and the small number indicates feet. For example, if you see a spot depth of a large 3 followed by a small 4. This indicate a depth of 3 fathoms and 4 feet, or 22 feet, as one fathom is six feet.
Sounding in meters indicates that soundings are in meters and decimeters. For example you see a spot depth of a large 7 followed by a small 6. This indicate a depth of 7 meters and 6 tenths of a meter.
You can convert between meters, feet and fathoms by using the depth conversion table provided on the chart.
The depths indicated on the chart are all based on Chart Datum. This could be the Mean Lower Low Water, or the Mean Low Water, or other tidal datum. To avoid grounding you have to take into consideration the height of tide and the tidal range.
