Big ball: aim for the biggest target
The second object ball is the target, and its size depends on where it sits. In the open it is about two ball-widths wide. Near a cushion it can be twice that. Finding the big ball is often the biggest single factor in choosing a shot.
Why a ball in the open is two balls wide
The cue ball scores if any part of it touches any part of the second ball. Their centres can be up to one ball-diameter apart, on either side, so the cue ball's path can be anywhere in a band two ball-widths wide. That's the target for a ball in the open.
Why a ball near a cushion is bigger
Put the same ball a short distance off a cushion. Now the cue ball can still hit it directly, but it can also miss it on the cushion side, go into the cushion, and hit it on the way out. Those two windows add up. A ball about one ball off a cushion, and best of all one ball off each of two cushions near a corner, can be a target three, four or more ball-widths wide.
There's a limit: frozen to the cushion, a ball gets smaller again, because the cue ball can no longer get between it and the rail. The sweet spot is a little off the cushion, not on it.
How to use it
- Look at the second ball before the first. When you scan a position, ask which ball near a rail could be your target, then work backwards to a hit that sends the cue ball there.
- Choose the end of the route. Two routes can reach the same ball from different directions. The one coming into the cushion side of a big ball has a wider window than the one approaching from the open table.
- Use reverse on the last cushion if it helps. Normally prefer running english, but a little reverse on the final cushion can bring the cue ball in along the rail onto a big ball. See Running and reverse english.
- Count in balls. Get used to thinking "this ball is three balls wide from here". The engine does exactly that: it measures each route's target in ball-widths, and a route ending on a three- or four-ball target ranks well above one ending on a free ball.