Which term describes estimating position when a recent position fix is not available?

• A. GPS Fix
• B. Radar Fix
• C. Triangulation
• D. Dead Reckoning

Answer: (D)

When you don’t have a recent position fix, you estimate your current location by advancing from the last known position using your speed, course, and the elapsed time. This is dead reckoning. You calculate the distance traveled (speed times time) and plot that distance along your course from the last fix. Because currents, leeway, and wind can push the bow or drift you off course, you account for possible drift and routinely update with a new fix to correct the estimate. The longer you go without a fresh fix, the larger the potential error becomes, so dead reckoning is most reliable for shorter intervals. GPS fixes give a current position from satellites, radar fixes determine position from radar data to known objects, and triangulation uses multiple bearings to locate you; none describe the ongoing projection from a last fix the way dead reckoning does.