For what kinds of shots can the 30° rule be used?
The 30° rule is very useful for:
- scratch avoidance
- carom shot aiming
- cluster busting
- obstacle avoidance
- position play
Here are some important things to keep in mind:
- The 30° rule applies only for natural roll shots.
- The 30° rule applies for the entire range of cut angles between 1/4-ball and 3/4-ball hits. This range includes the 1/2-ball hit (which is at the center of the range).
- The cue ball always leaves initially along the tangent line, which is 90° away from (i.e., perpendicular to) the impact line (AKA object ball direction, line-of-centers, target line, etc.). However, for slow to medium speed natural roll shots, the cue ball deflects to the 30° direction almost immediately (i.e., the curve in the trajectory is almost imperceptible). Only at higher speeds does the travel down the tangent line become significant (e.g., see NV 3.8 vs. NV 4.20). For more info, see the following demonstration from Vol. I of the Video Encyclopedia of Pool Shots:
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