🔍 Key Concepts

• Difference between chart datum (sounding datum) and tide height • How soundings (numbers on the chart) are measured and what they represent • Distinction between depth below datum and water level above datum

💭 Think About

• Ask yourself: What do the depth numbers printed on a nautical chart represent before you apply the tide correction? • Which option describes only the fixed, surveyed distance related to the seabed, and which options mix in changing water levels (tides)? • How would you use charted depth and the predicted tide height separately to find the total depth of water at a given time?

✅ Before You Answer

• Identify which choices refer to changing water level (tides) versus a reference level that stays fixed on the chart. • Check which option best matches the idea of a surveyed depth from a reference plane to the seabed, with no tide added. • Verify you understand that to get the actual depth at a given time, you normally combine charted depth with tidal height, rather than having them combined in the definition itself.