Backstaff – Davis Quadrant c.1730 England

Backstaff - Davis Quadrant

Backstaff – Davis Quadrant, scales engraved on boxwood arcs, c.1730 .
When using the cross-staff the observer is obliged to face the sun, which inevitably dazzles him. Davi´s quadrant alows the observer to turn his back to the sun.
The cross-staff is therefore more suited to measurements of the altitude of stars at night.
The Davi´s quadrant or back-staff, invented by the famous English navigator in 1594.

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