Chart No. 1 · I 10
Sounding (charted depth)
Depths & contours
A plain figure on the water is the depth below chart datum at that spot, in the chart's stated units.
What it means
A number printed on the water area is a sounding: the depth below chart datum. A small subscript digit is a decimal — 3₅ means 3.5. Upright figures are in true, surveyed position.
Why it matters
Always check the chart title block for the unit (meters, feet, or fathoms) before trusting any sounding — the same '3' can mean 3 m or 3 ft. Chart datum is a low-water level, so the real depth is usually more, never rely on less.