An ebony staff and four vanes of pear wood. The sky-end of the staff is pyramid-shaped. Vane one is fitted with a brass aperture disk, vane four has a brass horizon (a replacement). The brass pressure plates are missing from of vanes one and three; all four vanes have clamping screws.
Maker: Gerard Hulst van Keulen
Origin: Amsterdam, The Netherlands
Signed (stamped) on side one: G.H.V.K. * AMST: *
Dated (stamped) on side two: * 1788 *
Marked (stamped) on the staff and all four vanes: 4
The scales are from 90° to 38° (side one); from 90° to 28° (side two); from 90° to 12° (side three) and from 90° to 6° (side four) vice versa on all four sides (for zenith distance). The maximum reading accuracy is 10' for side one, and 5' for sides two to four.
Length of the staff 805 mm, width 18 by 18 mm; the vanes are 526, 375, 151, and 75 mm in length.
Leiden Observatory D1