RARE! G. Henneberg Patent 1897 Plumb & Level with Siding Vial Covers

A very rare level patented on Nov. 30, 1897 by Gustav Henneberg of New York, N.Y. Sliding brass covers for the level and plumb vial are simultaneously operated by a rod that passes through the two-piece stock. Pull out the brass tipped rod and the covers expose the vials. Push it in and the vials are covered and protected. A cleaver and gizmo-ish design, but it clearly didn’t catch on. This is the only example I’ve seen.
L: 18″