You’re probably familiar with the Snellen Eye Chart. Although largely replaced by the LogMar Chart in recent years, the Snellen Chart, developed in 1862, was long the standard way for measuring visual acuity. Visual acuity is described as the ability to see detail, or the resolution of your vision. It is measured in angles, and is dependent on the position of visual receptors in the retina. That big “E” on the eye chart was designed with a careful geometry to accurately measure those angles at a particular distance.
The video below takes the Snellen Chart and demonstrates its functionality at scale, measuring visual acuity across the San Francisco Bay.