Short discussions of the sextant began appearing in physics texts in the 1880s, and inexpensive sextants suitable for pedagogical purposes followed soon thereafter. This die-cast metal instrument is of that sort. Welch catalogs describe it as a "convenient demonstration model of an engineer’s or a mariner’s sextant." The scale is graduated every 30' from 0o to 120o and read by vernier to six minutes of arc. A small bubble level is mounted on the sighting tube.
Ref: W. M. Welch Scientific Company, Catalog. Scientific Apparatus (Chicago, 1929-1963).
W. M. Welch Scientific Company, "Instructions for the Use of No. 3536 Sextant Model."