How do “spot-on-the-wall” kicking systems work?
More information, including guidelines on how far the spot should be from the table, can be found in “VEPS GEMS – Part XIV: ‘Spot-on-the-Wall’ System” (BD, February, 2011).
There are different “rules of thumb” for estimating the best distance to the spot on the wall, but they don’t always match the results in the article very well. Here’s a common rule that does a decent job (although, it predicts a distance longer than recommended for a 3-rail shot and a distance shorter than recommended for a 1-rail shot):
from Monte Ohrt:
For any given spot-on-the-wall kick shot, the exact optimal distance from the first rail to the spot is the distance the cueball travels after it hits the first rail to the target. For a one-rail kick, this is simply the distance from rail 1 to the target. For a two-rail kick, it is the distance between rail 1 and 2, and also add the distance between rail 2 and the target point. For a three rail kick, it is the distance between rails 1 and 2, 2 and 3, and 3 to the target point … and so on for 4 rails, 5 rails, etc. After about 3 rails the point of convergence is so narrow that it normally doesn’t make any difference, just pick a spot at least 3 tables away.