 
Summary: David Alciatore ("Dr. Dave") ILLUSTRATED PRINCIPLES
"Draw Shot Primer Part III: using the trisect system"
Note: Supporting narrated video (NV) demonstrations, highspeed video (HSV) clips, and
technical proofs (TP) can be accessed and viewed online at billiards.colostate.edu. The
reference numbers used in the article (e.g., NV 3.8) help you locate the resources on the
website. If you have a slow or inconvenient Internet connection, you might want to view
the resources offline using a CDROM. See the website for details.
This is the third article in a series dealing with draw shot principles. In the last two months,
we explored some of the basic physics of draw shots and compared various aiming systems for
predicting the path of the cue ball. This month, we'll look at the trisect aiming system in more
detail. In particular, we'll look at an easy way to implement the system using your hand for
visualization.
Diagram 1 illustrates the trisect system. The cut angle (A) is defined as the angle between
the aiming line and the impact line. As summarized in Principle 29, for a "typical" draw shot, with
good action, the angle between the final cue ball direction and the impact line (2A) is twice the cut
angle (A). Therefore, the total angle between the aiming line and the final cue ball direction is
threetimes the cut angle (3A = A + 2A). The impact line trisects (divides by one third) the total
angle (i.e., A is 1/3 of 3A). That's why I call the method the trisect system. It could also be called
the doubleangle or twicetheangle system since 2A is twice A. (NOTE  In last month's article,
Principal 29 and the right side of Diagram 4 had a slight error. The angle "A" wasn't measured
