This gnomon is like those used on the lunar surface by Apollo astronauts during their scientific and photographic tasks. A gnomon is a gimbaled stadia rod mounted on a tripod so that the rod was free to point vertically. When deployed on the lunar surface, the shadow cast by the staff indicated sun angle and, therefore, direction. The rod length and the painted scale provided a reference for estimating the sizes of nearby objects. Shades of gray on the rod ranged in reflectivity from 5% to 35% and a color scale enabled more accurate determination of rock and soil colors by comparison.
The gnomon configuration was a little different for each Apollo flight. This particular gnomon was qualified for flight, but never used on a mission. It is similar to the one used on the early lunar missions (Apollo 11, 12, and 14) because it has color scales affixed to the rod and not the legs.
NASA transferred this to the Smithsonian in 1974.