Old instruments
Assumed Position
Direct answer
Assumed Position is a convenient nearby latitude and longitude selected to simplify a celestial calculation.
Assumed Position is a chosen sight-reduction coordinate used in historical astronomy, timekeeping, or navigation.
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At a glance
- Found in
- Historical Almanacs & Instruments
- Related
- Local Hour Angle, Greenwich Hour Angle, Observed Altitude, Computed Altitude
Assumed Position is a chosen sight-reduction coordinate used in historical astronomy, timekeeping, or navigation.
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The story behind Assumed Position
Assumed positions made tabular sight reduction faster by aligning chosen values with available integral arguments.
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Why Assumed Position matters
Assumed Position matters because the intercept method does not require the computed point to be the navigator's exact estimated position.
Assumed Position in practice: an example
A navigator selects whole-degree latitude and a longitude that makes local hour angle an exact degree.
Where readings of Assumed Position go wrong
It is a mistake to plot the resulting position line from the dead-reckoning point when the calculation used a different assumed position.
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
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Common questions
What is an assumed position?
Assumed Position is a convenient nearby latitude and longitude selected to simplify a celestial calculation.
What do people get wrong about an assumed position?
It is a mistake to plot the resulting position line from the dead-reckoning point when the calculation used a different assumed position.
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