From the US National Library of Medicine: "[Mayerle's] eye chart ... combined four subjective tests done during an eye examination. Running through the middle of the chart, the seven vertical panels test for acuity of vision with characters in the Roman alphabet (for English, German, and other European readers) and also in Japanese, Chinese, Russian, and Hebrew. A panel in the center replaces the alphabetic characters with symbols for children and adults who were illiterate or who could not read any of the other writing systems offered. Directly above the center panel is a version of the radiant dial that tests for astigmatism. On either side of that are lines that test the muscular strength of the eyes. Finally, across the bottom, boxes test for color vision, a feature intended especially (according to one advertisement) for those working on railroads and steamboats." (Image source: US National Library of Medicine)