Snellen Vision Testing Cards Set for Railway, Marine and School Exams, Early 20th C. pretty abacus The scalene triangle is marked

The scalene triangle is marked with a Sphynx logo

11 5/8" x 8 1/4" x 9/16

I am pricing just based on its charm

with glossy front

A few small edge chips here and there and a little a little greening to the brass pins

Snellen Vision Testing Cards Set for Railway, Marine and School Exams, Early 20th C. pretty abacus The scalene triangle is markedFound in their original envelop, with Millar and Wel_ (?) Opticians on, Boston stickeron the face and instruction card still inside, this appears to be a complete, or nearly so, set of early 20th c. Snellen vision testing cards. Nineteen cards total, plus instruction card, with three of the cards showing railway signals to be read at a distance of 20 feet as these were commonly used for testing the vision of train conductors railway workers. Included: