Because the opening between the two sides of E is the smallest, the resolution of the human eye is the most tested.

The Angle of view at which the normal eye can distinguish the smallest object (or distinguish the nearest two points) is called the minimum Angle of view, and the minimum Angle of most normal eyes is the one-minute Angle of view. At a distance of 5 meters, the opening between the upper and lower sides of line 1.0 E on the eye chart is just one minute of the normal eye Angle (the opening of C on the eye chart is the same). The Angle of view of the smallest object (or the two points that distinguish the nearest point) is called the minimum Angle of view, and the minimum Angle of view of most normal eyes is a one-minute Angle of view. At a distance of 5 meters, the opening between the upper and lower sides of line 1.0 E on the eye chart is just one minute of the normal eye Angle (the opening of C on the eye chart is the same).