Stand and hold the Brock string with beads placed so that the farthest bead is just in front of your thumb when your arm is extended, the second bead is in the middle of the string and the closest one at a point where you can see a single bead (without seeing double). Look at the farthest bead, it should appear as one bead with two strings going into it, when you look at the center bead, you should perceive two strings going in, and two strings going out. When you look at the closest bead, you will see two strings going out from the bead.
This is a phenomenon of physiologic double vision, the bead you are looking at will be in focus, but it will seem as if the other beads become double. Your goal is to have good focus on one bead at a time. This may make you feel dizzy or lightheaded, but should improve as you repeat the exercises
