The donor states that it was used from the 1920s through to the 1940s; identical item on website dated to 1930s.
Measurement numbers from 1 to 180 degrees going both ways on the circular edge; "No 19 // THE L.S. STARRETT CO. // ATHOL. MASS. U.S.A." engraved on the protractor; "READ INSIDE SCALE // READ OUTSIDE SCALE" written in pen on a piece of tape on the handle
Inscribed on centre of dial: "L.S. STARRETT ATHOL, MASS. U.S.A. // PAT. APRIL 15, 1897"; metal indicator is calibrated 10 to 100 and 100 to 10; lid of box has, "Red - Labelled No. 107 STARRETT // Registering Speed Indicator // MADE BY".