Old instruments
Dead Reckoning
Direct answer
Dead Reckoning is the process of advancing a known position using courses steered, speeds, and elapsed time.
Dead Reckoning is a course-and-speed position estimate used in historical astronomy, timekeeping, or navigation.
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At a glance
- Found in
- Historical Almanacs & Instruments
- Related
- Pelorus, Celestial Navigation, Latitude by Meridian Altitude, Longitude by Chronometer
Dead Reckoning is a course-and-speed position estimate used in historical astronomy, timekeeping, or navigation.
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The story behind Dead Reckoning
Dead reckoning long predates electronic navigation and was often recorded with logs, glasses, and traverse boards.
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The Book of the Sky
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Why Dead Reckoning matters
Dead Reckoning matters because it supplies a continuous estimate between external fixes and a starting point for sight reduction.
How to read Dead Reckoning
Dead Reckoning by logging every course, speed, time interval, and known correction speaks to current, leeway, or maneuver.
Dead Reckoning in practice: an example
A vessel travels 10 nautical miles on a true course and plots that displacement from the last fix.
Where readings of Dead Reckoning go wrong
Unmeasured current, wind, steering error, and log error accumulate with time, so the result is not a fix.
Sources and editorial method
Research references used for this entry include:
- National Geospatial-Intelligence Agency: The American Practical Navigator - Official modern reference for navigation principles, celestial observations, sight reduction, and navigational tables.
- Royal Museums Greenwich: Traverse Board - Museum documentation of the peg board used to record a vessel's course and speed by watch.
- Source
- The Great Almanac Dictionary
- Category
- Historical Almanacs & Instruments
- Last updated
- 2026-09-26
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More in Historical Almanacs & Instruments
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- Lunar Distance Method
- Planisphere
- Semidiameter Correction
- Transit Table
- Assumed Position
- Celestial Globe
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Common questions
What is Dead Reckoning?
Dead Reckoning is the process of advancing a known position using courses steered, speeds, and elapsed time.
What do people get wrong about Dead Reckoning?
Unmeasured current, wind, steering error, and log error accumulate with time, so the result is not a fix.
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