One shot will be reviewed over and again, with the player using a different method each time. The shot angle chosen is the half ball hit, one of the most frequent cut shots (angled shots where the cue ball, object ball and pocket are not in a straight line) taken in pool.
The half ball reference will be explained below under "fraction aiming".
CAUTION: Aim systems will be named as plural in this manual as there are subtle variations of each in wide use, and this manual represents a primer introducing the player to each type of aim methodology or style.
CAUTION: All discussions of aim in this manual are given in their simplest physical terms. Since English or sidespin will not be employed, the effects of spin-induced throw, ball "swerve" and cue "squirt", etc. (factors which may cause a straight aimed and stroked shot to not roll straight) will be discounted from discussion. Collision-induced throw will be discussed only briefly. It will also be assumed the cue ball will roll along the cloth rather than jump from its surface.
"The First Aim System" - Aim by Instinct
A plurality of amateurs and even some professional players use no geometric aim system but aim by mere instinct.
Limitations of Aiming by Instinct:
1. Most amateurs who aim by instinct miss often. Those playing professionals who aim by instinct usually had begun with some system, but after stroking millions of shots over many years of practice, have internalized aim calculations so they need not instruct themselves on imagined aim lines and points.
2. There is no point of reference to discuss shot making without a system. Pool instructors use the systems in this manual as aids for diagramming shots for training and assessment. The sole thing an instinct player can discern on a miss is whether they overcut or undercut a ball, and then with scant frame of reference for future correction.
Fraction Aim Systems
Fraction aim describes quantifying aim based on ball appearances at impact. To score a ball into a pocket:
1. Describe the relationship at impact between cue ball and object ball in terms of fractions of ball where they intersect (specifics are given below).
2. Plot the shot line to create the given fraction and aim the cue ball along this line.
The Aim Line
In the illustration, one portion of a pool table is shown surrounding a corner pocket. The #2 object ball (colored blue) is shown aimed to roll into Pocket A. It is resting on its base on the intersection of imaginary lines extended from the diamond markers adjacent to the corner pocket (Diamonds B and C). The cue ball has been placed further along the table off the diagram. The intended position of the cue ball at impact is shown, however, and is called the ghost ball at G.
CAUTION: Billiard balls are not shown to scale but are slightly larger for ease of comprehension. Actual balls may be placed on their bases as diagrammed, however, for aim practice on a real table.
The illustration accompanying this article explores the key concepts of aim line (the "line of centers") and the contact point. The line extended from the center of the pocket opening through the base of the object ball and beyond is called the "aim line".
The aim line is also often called the line of centers as a second ball will be driven there, with both balls centered on the line at their bases at impact. A cue ball that strikes position G will propel the object ball to the pocket.
The unique point on the object ball where the cue ball touches it is called the "contact point". The contact point in the diagram is that spot on the 2-ball's equator that is furthest from the pocket opening where the ghost cue ball and 2-ball touch. The corresponding point of impact on the cue ball is called the cue ball point.
CAUTION: Pool is a game of precision and therefore a game of misses. Rolling the base of the object ball so that it will cross the center of the pocket opening allows for the greatest possible miss to either side of the line while still pocketing successfully. Average corner pockets are 2¼ times the width of a ball to provide this freedom.
Aim Primer 1: How To Use The Aim Manual
Aim Primer 2: Glossary Of Key Terms
Aim Primer 3: Stance And Stroke
Aim Primer 4: Instinct Vs. Fraction Aim
Aim Primer 5: Contact Point And Half Ball Line
Aim Primer 6: Fraction, Edge-To-Edge, Perfect And Ghost Ball Aim
Aim Primer 7: Ghost Ball Vs. Contact Point Aim
Aim Primer 8: Parallel And Pivot Aim