🔍 Key Concepts

• Tidal datum (chart datum): the reference level from which tidal heights are measured • Difference between depth of water and the reference level vs. difference between high and low water • How tide tables report height of tide at a given time

💭 Think About

• Ask yourself: In tide tables, when they list a height like “+5.3 ft,” what exactly is that measured above or relative to? • Which choices describe a vertical difference from a reference level, and which describe something else (like total range between high and low)? • Think about how you would use height of tide together with charted depth to find the actual depth of water under your keel at a given time.

✅ Before You Answer

• Identify which option clearly mentions a reference level or datum as the baseline for the measurement • Make sure the option you pick could be used directly with a charted depth to compute total water depth • Eliminate any options that describe the total range between high and low water, instead of the height at one specific time.