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The Snellen chart is a widely used tool for measuring visual acuity. Named after the Dutch ophthalmologist Herman Snellen, who created it in 1862, this chart helps assess eyesight. To get started, choose a vertical surface to display the chart, stand 6 meters away, and aim your device’s rear camera at the surface. Once the chart loads, you can adjust its position and size via the control panel or directly on the screen using drag-and-drop, rotate with two fingers, or zoom in/out gestures. Need to switch surfaces? Just tap the button with the two circular arrows. You can also mute the sound or hide help texts using the appropriate buttons.