PD: If you have glasses, take them off and position a card with a magnetic strip under your nose. Look straight into the camera and take a picture.

PD: Move and zoom the picture so that it matches the lines as much as possible.

PD: Move the circle on the center of the eye, like shown in the video.

PD: Repeat for the other eye.

PD: Move the ruller on the edge of the card, like shown in the video.

PD: Repeat for the other edge.