Educational contact goniometer with fixed arms

manufacturer
Contact goniometer (plastic 10.8 x 6.4 cm) with an instruction leaflet (12.7 x 15.2 cm) in beige paper envelope (16.6 x 9 cm) .
Signed "WARD'S | CONTACT GONIOMETER | WARD'S NATURAL SCIENCE | (800) 962-2660 | Made in U.S.A."
2nd half 20th century.

private collection