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This original Keystone Diagnostic Series stereometric training card, marked DC-41, was part of the Keystone Aviators’ eye-training system used to evaluate depth perception, visual alignment, and acuity for pilot readiness.
The front shows two aircraft illustrations with three numbered vertical test columns containing letters used for stereoscopic alignment. The reverse side provides a printed aircraft diagram divided into sections labeled for “Letter Standing Forward,” “Visual Acuity Required,” and percentage-based columns for pilot visual assessment.
Produced by Keystone View Company, Meadville, Pennsylvania, this card is part of the DC-31 to DC-53 aviators’ diagnostic series and was used in professional training, making it an excellent collectible for aviation, optical, and instructional history enthusiasts.
Condition:
Very good vintage condition with mild surface handling signs but no major damage. Cards of this type often show wear from instructional use; this example remains clean and well-preserved.
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