(1) Need to improve your aim? You probably already have the tools to help on your table. Place any ball dead center of the jaws of a side pocket. Now, place a chalk block on both sides of the ball about 1/2" from the edges. Remove the ball.
Now place an object ball on the center spot. With a center hit on the cue ball from each of the positions illustrated, try to sink the object ball in the side without touching the chalk. When it becomes easier, tighten the "gate" by moving the chalk closer together. It is a good idea to practice this from both sides of the table to keep your right and left cut shoots equally strong.
(2) The "window" referred to is the maximum angle you are able to get off the rail with spin. It is a good idea to be familiar with your "personal" window. Try to sink the cue ball cross corner from the positions shown (small balls). Refer to the corresponding large cue balls for an approximate cue ball hit. For extreme rebound angles, elevate the butt of the stick and use a little bottom with the right side spin (The cue ball may curve a little). Shoot easy. Knowing your window can help you beat a safety or self imposed hook. This is also a good test for your tip and stroke.
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