A Brock string is simply a piece of white string, usually 3-4 feet (1-1.2m) long, with four movable color beads placed on it. One end can either be tied to a distant object, such as doorknob, or held by supervising person. The other end (whichever, it does not matter) is held to the tip of the nose. The beads should be positioned evenly from the first near the nose starting at approximately 10-15 inches (25-35cm).
Note that when evaluating an athlete, it is appropriate to place the string in a position that relates to his sport. For example, instead of placing the distant end of the string on a door knob in the straight ahead position as you would for a baseball player, move it down to the floor for a hockey player, or place one end up at ten feet high for a basketball player. To accomplish this, a 20 feet string may be needed and is available.
When the subject looks at the first bead, he or she should see one bead with two short strings leading toward it and two longer strings leaving it. On the two strings which leave the bead there will be 3 pairs of beads.
Next, have the subject look at the second bead or the one at the 25in distance from the nose. Here again the subject should see two strings entering the bead and two strings leaving it, making a large “X”. This will also mean that there are two beads ahead of and two behind the single second bead.
Finally, look at the one of the last two beads. You should notice the two strings making a “V” toward the bead and crossing exactly at the bead. The two closest beads will be double. The door knob or whatever object the string was tied to may also appear doubled if there is adequate separation between it and last bead.