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The 'backstaff', or 'back-quadrant', is a navigational tool that was used to determine latitude. It worked the same way as the cross staff and astrolabe except instead of looking at the sun, users kept the sun to their back (hence the name) which prevented damage to their eyes.
The backstaff was invented by Captain John Davis in 1590.
The French called it the 'English Quadrant'.

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