back staff
noun
an obsolete instrument for determining the altitude of the sun by facing away from the sun, sighting upon the horizon, adjusting a cursor until its shadow falls upon the sight through which the horizon appears, and measuring the resulting arc.
Origin of back staff
First recorded in 1620–30
Words nearby back staff
back scratcher,
back seat,
back shaft,
back shift,
back slang,
back staff,
back stairs,
back story,
back straight,
back street,
back stretch
Example sentences from the Web for back staff
This instrument was known also as "the back-staff" from the position of the observer with his back to the sun when using it.
Life Aboard a British Privateer in the Time of Queen Anne |Robert C. Leslie