Betts Fusion Test 7F; Slide DB-5F (Keystone #35107)
Betts Fusion Test 7F; Slide DB-5F (Diameter of Balls, 10mm)
Stereo card from Keystone View Co.’s stereoscopic Betts Fusion Tests, ca. 1940. Corollary to his book The Prevention and Correction of Reading Difficulties, Betts Telebinocular Tests were commonly used by schools as a screening device for vision dysfunction—much to the chagrin of the American Medical Association, which found the test over-diagnosed vision impairment and deemed it "unacceptable."
Series slide DB, showing an increasing diameter of colored balls. Card slightly bowed, otherwise VG; 3.5 X 7 inches. Housed in mylar sleeve for safekeeping.