Old instruments
Running Fix
Direct answer
Running Fix is a fix formed by advancing an earlier line of position to the time of a later observation.
Running Fix is a motion-advanced position fix used in historical astronomy, timekeeping, or navigation.
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At a glance
- Found in
- Historical Almanacs & Instruments
- Related
- Line of Position, Celestial Position Fix, Local Hour Angle, Greenwich Hour Angle
Running Fix is a motion-advanced position fix used in historical astronomy, timekeeping, or navigation.
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The story behind Running Fix
Running fixes long supported coastal and celestial navigation under changing visibility or limited target geometry.
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Why Running Fix matters
Running Fix matters because it permits separated observations to be combined when simultaneous lines are unavailable.
Running Fix in practice: an example
A morning Sun line can be advanced to intersect an afternoon Sun line after applying vessel motion.
Where readings of Running Fix go wrong
Current, leeway, and steering errors enter the advanced line, so a running fix is not equivalent to simultaneous observations.
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.
- Source
- The Great Almanac Dictionary
- Category
- Historical Almanacs & Instruments
- Last updated
- 2026-09-26
Explore Running Fix
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More in Historical Almanacs & Instruments
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Common questions
What is a running fix?
Running Fix is a fix formed by advancing an earlier line of position to the time of a later observation.
What do people get wrong about a running fix?
Current, leeway, and steering errors enter the advanced line, so a running fix is not equivalent to simultaneous observations.
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