Always in the center
Three mirrors are mounted so that they form a corner. The mirror image is always in the center – no matter how you move in front of the mirrors!
The mirror image shows the relative strengths of the eyes. If the joint is in the middle between the eyes, the vision is equally strong in both eyes. If the mirror image is shifted to one side or the other, it shows that one eye dominates the other. If you look closely, you can see more mirror images. The one in the middle is upright, while the ones on the sides are mirrored.