After compiling his first star altitude curves that would simplify celestial
navigation aloft, P. V. H. Weems encouraged Bausch & Lomb to manufacture an improved model of the Bureau of Standards aircraft sextant for commercial use. This is one of those instruments. The U.S. Naval Observatory transferred it to the Smithsonian in 1948. The referenced patent is that issued to K. H. Beij in February 1929. A certificate of inspection in the box, dated June 1931, identifies this as a "Bu Stands Type Model C."
Ref: K. H. Beij, "Means for Determining Altitude," U.S. Patent