Signedon right prism housing: AO [in shield] / SPENCER
on door of case: AO [in shield]
on plaque on foot: JARRELL-ASH COMPANY / SCIENTIFIC INSTRUMENTS / BOSTON, MASS.
Inscribedon left prism housing: 289172
Primary SourcesSpencer Lens Company, Spencer Low Power Binocular Microscopes (Buffalo, NY: Spencer Lens Company, 1935).
American Optical Company, Spencer Scientific Instruments (Buffalo: American Optical Company, 1947), 132.