Is there a rule for predicting CB direction for a draw shot similar to the 90° rule for a stun shot and the 30° rule for a rolling CB shot?
Yes. It is called the trisect (or 3-times-the-angle) system, which applies to a “good action” draw shot for cut angles smaller than about 40° (i.e., ball-hit fraction greater than about 3/8). You can use a modified version of the Dr. Dave peace-sign technique, or your cue, or your fingers measuring distance to predict the final cue ball direction. Here are good video demonstrations, one from Vol. I of The Video Encyclopedia of Pool Shots:
Here’s another video, from Vol. II of the Billiard University (BU) Instructional video series, that shows how you can use the trisect system effectively when you have ball in hand:
And here’s an example from Vol. II of How to Aim Pool Shots (HAPS) showing how the trisect system can be used to aim non-ball-in-hand carom shots:
“Good action” draw is defined as what is required to make the CB turn perpendicular with a 1/2-ball hit:
This is called the 90° rule for “good action” draw, not to be confused with the standard 90° rule for stun shots.
For more information and demonstrations, see:
- “HAPS – Part IV: Draw Carom Shot Aiming” (BD, February, 2015)
- “Draw Shot Primer – Part III: using the trisect system” (BD, March, 2006)
- “Draw Shot Cue Ball Directions” (BD, December, 2011)
- where the CB goes for different cases
Here’s a convenient 1-page trisect system resource page summarizing the important concepts.
See also: shot speed effects.
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