Jacob's staff
calibrated wooden rod with sliding crosspiece used for measuring the altitude of celestial bodies or the height of distant objects
en-US/ˈd͡ʒeɪkəbz ˈstæf/
en-GB/d͡ʒeɪkəbz ˈstɑːf/
calibrated wooden rod with sliding crosspiece used for measuring the altitude of celestial bodies or the height of distant objects