Educational contact goniometer with fixed arms

Mohave, Hollywood
Contact goniometer (colorless clear plastic 20.3 x 10.2 cm) in card envelope (21.7 x 11.4 cm).
Signed "MOHAVE SALES INC.| HOLLYWOOD 27 | U.S.A. | EVERYTHING FOR ENGINEERS AND GEOLOGISTS | 77 - CONTACT GONIOMETER (AFTER PENFIELD)"
Fist half 20th century.

private collection