Old instruments
Davis Quadrant
Direct answer
Davis Quadrant is a backstaff with graduated arcs and vanes designed chiefly for measuring the Sun's altitude at sea.
Davis Quadrant is an arc-form backstaff used in historical astronomy, timekeeping, or navigation.
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At a glance
- Found in
- Historical Almanacs & Instruments
- Related
- Cross Staff, Backstaff, Octant, Reflecting Circle
Davis Quadrant is an arc-form backstaff used in historical astronomy, timekeeping, or navigation.
An engraved functional orientation; the page explains the real instrument, method, or publication.
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The story behind Davis Quadrant
Named for John Davis, the design was refined by later makers and used widely in seventeenth- and eighteenth-century navigation.
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Why Davis Quadrant matters
Davis Quadrant matters because its two-arc layout improved range and scale reading while preserving shadow-based observation.
Davis Quadrant in practice: an example
A mariner could observe meridian altitude without looking along a line aimed at the Sun.
Where readings of Davis Quadrant go wrong
A rolling horizon, worn scale, misplaced vane, or poor shadow edge can make the reading unreliable.
Sources and editorial method
Research references used for this entry include:
- Royal Museums Greenwich: Backstaff - Museum documentation of the backstaff, its arcs, vanes, scales, and solar-altitude use.
- Royal Museums Greenwich: Astronomical and Navigational Instruments - Museum reference collection for historical observing, calculating, timekeeping, and navigation instruments.
- 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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Common questions
What is Davis Quadrant?
Davis Quadrant is a backstaff with graduated arcs and vanes designed chiefly for measuring the Sun's altitude at sea.
What does the name Davis Quadrant mean?
Named for John Davis, the design was refined by later makers and used widely in seventeenth- and eighteenth-century navigation.
What do people get wrong about Davis Quadrant?
A rolling horizon, worn scale, misplaced vane, or poor shadow edge can make the reading unreliable.
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