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

with glossy front

without a chipped or cracked block that I can see

I am pricing just based on its charm

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

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: