Dr. Dave's answers to frequently-asked questions (FAQs), mostly from the AZB discussion forum

For more information, see the strategy resource page and Chapter 5 in The Illustrated Principles of Pool and Billiards, Vol. I and Vol. II of the Video Encyclopedia of Pool Shots (VEPS), Vol. I and Vol. II of the Video Encyclopedia of Pool Practice (VEPP), Vol. II of the Video Encyclopedia of Eight Ball (VEEB), and Vol. III of the Video Encyclopedia of Nine-ball and Ten-ball (VENT)

**30° and 90° rules**

*What are the 30° and 90° rules, and how can they be used for cue ball control?*

See 30° and 90° rules.

**45° rule for center-table position and routes **

*What is the 45° rule, and how is it used to position the CB at or through the center of the table?*

It states that if the CB rolls into the short rail at close to a 45° angle, it will head off two rails fairly close to the center of the table. For more info, see the following demonstration from Vol. II of the Video Encyclopedia of Pool Shots (VEPS):

See "VEPS GEMS - Part III: English and Position Control" (BD, March, 2010) for more information. Here's another good video demonstration of how the 45° rule is applied at the table:

Here's a good drill from Vol. II of the Video Encyclopedia of Pool Practice (VEPP) for practicing getting to the center of the table off pocket hangers:

See "VEPP – Part V: Hanger Table-Center Drills," (BD, August, 2012) for more information.

The position play principles handout has some examples of leaving an angle, coming into the line of a shot, and applying the 45° rule.

*How does the cue-ball-control clock system work?*

Here's a good clock system handout (and diagram below) illustrating the basics. Buddy Hall does a good job of explaining and demonstrating the clock system in the following video: Buddy Hall's clock system.

This system is a good reference for known shots like this. For other shots at different angles and distances to the rails, things will vary some. Cloth and cushion conditions also affect how well the system applies.

**drills for practicing cue ball control and position play**

*What are some useful drills for getting better at cue ball control and position play?*

The following drills are excellent for learning and improving cue ball control and position play:

- Billiard University (BU) playing-ability exams
- line-of-balls drills
- "playing the ghost" rating drills
- position control drills
- target practice drills
- 3-ball drill
- wagon wheel drills

Drills for working on other skills can be found on the drills resource page.

*What are best ways to play end-game patterns?*

See the following excerpt from Vol. III of the Video Encyclopedia of Nine-ball and Ten-ball (VENT):

For more info, see "VENT – Part VI: End-Game Patterns" (BD, March, 2018).

**leaving an angle on a shot and coming into the line of a shot**

*How do I do this?*

See the following demonstrations from Vol. III of the Video Encyclopedia of Eight Ball (VEEB) and from Vol. II of the Video Encyclopedia of Pool Shots:

Here are some additional good examples:

Sometimes, it is important to play for a precise point or line, rather to a general area. Here's an example from Vol. III of the Video Encyclopedia of Pool Shots:

The position play principles handout has some examples of leaving an angle, coming into the line of a shot, and applying the 45° rule.

*How can I get position on the next shot if the current shot is nearly straight in?*

See : NV B.30 - Cue ball position control with nearly straight-in shots.

And here are some examples from Vol. III of the Video Encyclopedia of Eight Ball (VEEB):

For more information, see: "VEEB - Part VI: Straight-In Shot Options" (BD, April, 2016).

*How do I avoid a scratch in different situations?*

See the following video demonstrations:

- NV 3.7 - Using the 90° rule to check for and prevent a scratch
- NV 3.10 - Using the 30° rule to check for and prevent a scratch
- NV 4.2 - Using a draw shot to prevent a scratch
- NV 4.5 - Using a follow shot to prevent a scratch
- NV 4.22 - Avoiding a tangent-line scratch using slow speed
- NV B.25 - Using draw and sidespin to beat a scratch in a side pocket, with Tom Ross
- NV B.31 - Using inside english and follow to beat a scratch and get down-table position
- NV B.46 - Cue ball path scratch avoid, cluster break-out, and billiard (carom) examples
- NV J.14 - Top 10 Pool Shots Amateurs Play Wrong … and How to Play Them Right
- HSV B.12 - Beating a scratch by bouncing the cue ball off the rear rim of a pocket

*What effect does shot speed have on the 90° and 30° rules?*

Shot speed has no effect on the 90° rule. With a stun shot, the CB heads straight down the tangent line, regardless of speed.

With follow and draw shots, the CB persists along the tangent line longer before curving to the final direction, as demonstrated in this video:

Follow and draw are delayed even more if the CB hops into the OB. For more information and demonstrations, see the ball hop effects resource page.

When using the 30° rule, this diagram shows how you need to shift the peace-sign down the tangent line with faster speeds, to predict the final CB direction:

For more information, see "90° and 30° Rule Follow-up - Part V: the final chapter" (June, 2005).

With draw shots, a similar shift with speed occurs, based on this diagram:

For more information, see "Draw Shot Primer - Part I: physics" (January, 2006).

The condition of the cloth also has an effect. With a slicker cloth, the CB persists along the tangent line longer before curving to the final direction. For more info, see cloth effects.

*How do you predict CB direction when the CB doesn't have stun, complete forward roll, or close to maximum draw?*

For a stun shot, the 90° rule applies. For a rolling CB shot, the 30° rule applies. For a "good action" draw shot, the trisect system applies. For shots in between all of these different cases (i.e., "tweener" shots), the cue ball will go somewhere in between the indicated directions. The only way to get a feel for how much "in between" the cue ball will go is to practice ... a lot! However, knowing the reference directions and how they correspond to different tip positions can help you judge the tip positions required for different CB directions, as demonstrated in the following video from Vol. I of the Video Encyclopedia of Pool Shots (VEPS):

For more info, see Vol. I and Vol. II of the Video Encyclopedia of Pool Shots (VEPS) and:

- NV C.5 - Wagon wheel cue ball control drill, from VEPP II
- NV B.43 - Cue ball position control stun, roll, and draw reference lines
- NV B.46 - Cue ball path scratch avoid, cluster break-out, and billiard (carom) example
- "Fundamentals - Part V: CB position control" (BD, January, 2009).
- "Fundamentals - Part VI: CB control examples" (BD, February, 2009).

To see how speed and table conditions affects CB trajectories, see speed effects.

For more information, see where the CB goes for different types of shots.

*How can I know where the cue ball will go on every type of shot?*

Below is an illustration of reference directions useful for predicting the path of the CB. For more information, see the video and links below.

Here's a good video demonstration of the reference directions predicted by the 90° rule (for a stun shot), the 30° rule (for a follow shot), and the trisect system (for a draw shot):

See also:

- NV B.44 - Dr. Dave 30°-rule peace-sign hand calibration
- NV B.45 - Cue ball path speed effects
- NV B.46 - Cue ball path scratch avoid, cluster break-out, and billiard (carom) examples
- NV B.60 - Mike Page's Cue Ball Control
- NV B.66 - The 30° rule, from VEPS I
- NV B.67 - The trisect system for draw shots, from VEPS I

Here's an example from Vol. I of The Video Encyclopedia of Pool Shots where the reference lines can be useful to plan cluster break-out shots:

For more info, see:

- where the CB goes for different cases
- "Fundamentals - Part V: CB position control" (BD, January, 2009)
- "Fundamentals - Part VI: CB control examples" (BD, February, 2009)

*where the CB goes for different types of shots*

*Where will the cue ball go after it hits an object ball?*

**For a good basic tutorial with demonstrations of most of the stuff below, see the CB control tutorial page first.**

For a **stun shot**, most people know the right answer: in the tangent line direction, perpendicular to the OB direction. This is the *90° rule* (see "The 90° rule: Part I - the basics" - BD, January, 2004). If you want a more precise answer that accounts for various effects (e.g., friction and english), see the following instructional articles:

"90° and 30° Rule Follow-up - Part II: speed effects" (BD, March, 2005).

"90° and 30° Rule Follow-up - Part III: inelasticity and friction effects" (BD, April, 2005).

"90° and 30° Rule Follow-up - Part IV: english effects" (BD, May, 2005).

"90° and 30° Rule Follow-up - Part V: the final chapter" (BD, June, 2005).

FYI, here is a convenient one-page summary of the 90° rule.

For a **rolling CB**, the cue ball changes direction by about 30° for a wide range of cut shots (1/4 to 3/4 ball hit). This is the *30° rule* (see "The 30° rule: Part I - the basics" - BD, April, 2004). If you want to be more precise, the angle is a little more (about 34°) closer to a 1/2-ball hit and a little less (about 27°) closer to a 1/4-ball or 3/4-ball hit (see TP B.13 for even more details and precision). If you want to know how to account for speed effects, see "90° and 30° Rule Follow-up - Part V: the final chapter" (BD, June, 2005). If you want an easy way to use your hand to accurately visualize the cue ball direction, use the Dr. Dave peace-sign technique. FYI, here is a convenient one-page summary of the 30° rule.

For a **draw shot** with good draw action, and for cut angles smaller than about 40° (i.e., ball-hit fraction greater than about 3/8), the *trisect system* is your answer (see "Draw Shot Primer - Part III: using the trisect system" - BD, March, 2006). You can use a modified version of the Dr. Dave peace-sign technique to predict the cue ball direction (see the article, NV B.43, and NV B.67 for illustrations and examples).

For shots **"in between"** all of these different cases (i.e., "tweener" shots), see tweener shots.

To see how speed and table conditions affects CB trajectories, see speed effects.

For more info, see Vol. I and Vol. II of the Video Encyclopedia of Pool Shots and:

- NV D.11 - Cue Ball Control Target Pool Drill - from Vol-II of the Billiard University instructional video series
- NV C.5 - Wagon wheel cue ball control drill, from VEPP II
- NV B.73 - Leaving an angle and coming into the line of a shot, from VEPS II
- NV B.74 - Center-of-table position and routes, with the 45° rule, from VEPS II

- NV B.75 - 30°-rule natural-angle examples, from VEPS III
- NV B.43 - Cue ball position control stun, roll, and draw reference lines
- NV B.44 - Dr. Dave 30°-rule peace-sign hand calibration
- NV B.45 - Cue ball path speed effects
- NV B.46 - Cue ball path scratch avoid, cluster break-out, and billiard (carom) example
- NV B.60 - Mike Page's Cue Ball Control
- NV B.66 - The 30° rule, from VEPS I
- NV B.67 - The trisect system for draw shots, from VEPS I
- NV B.68 - Tweener cluster breaks, from VEPS I
- "Fundamentals - Part V: CB position control" (BD, January, 2009).
- "Fundamentals - Part VI: CB control examples" (BD, February, 2009).

See also:

- the rail cut shot position control
- Ralph Eckert's lessons on natural-roll position-play reference lines (part 1, part 2, part 3)

*What if the cut is very thin or hit very full?*

For roll shots, there are good approximations for the CB deflection angles.

For a fairly **full hit**, with a ball-hit-fraction greater than 3/4, the CB will deflect about 3-times the cut angle.

For a fairly **thin hit**, with a ball-hit-fraction less than 1/4, the CB will deflect about 70% of the angle between the aiming line and the tangent line.

See "Rolling Cue Ball Deflection Angle Approximations" (BD, November, 2011) for illustrations, examples, and more information.

There are similar rules for draw shots. For more information, see "Draw Shot Cue Ball Directions" (BD, December, 2011).

As with the 30° rule and trisect system, the full-hit and thin-hit rules apply to the final direction of the CB. The actual final path of the CB is shifted down the tangent line with higher speed.

Video demonstrations of these types of shots can be found in Vol. I of the Video Encyclopedia of Pool Shots.

**from Neil Murphy** (Toronto, Canada) via e-mail:

**Neil's Unified CB Control Theory**

As my aiming system, I start each shot along the target line of the shot, and mentally create a rectangle between the contact point of the cue ball and the contact point of the object ball (see the diagram below).

I started exploring how to predict where the natural angle of a rolling cue ball would go. I extracted deflection angles from one of your charts in your technical papers and put them into a spread sheet. I calculated where the natural angle would intersect the line below the cue ball, if extended backwards. For all angles from 0-85°, the natural angle extends backwards and cuts the vertical line below the cue ball consistently at the 30% mark.

But what about draw shots? I extracted deflection angles from one of your charts and started playing with the geometry on my spread sheets. What if I extend the draw angle back the same way I did the natural rolling shot? Again the height of the division is near 30% of the total vertical axis! In this case we are closer to a 1/3, but given the greater degree of variability in draw shots, 30% is an excellent estimation and provides better visual symmetry when lining up the shots.

So now we have a system that allows us to accurately predict the cue ball path. By standing perpendicular to the target line, you can see the shots accurately. However, most shots you can get a reasonable estimate facing down the target line as well. It is also possible to view this in other ways. I will sometimes visualize the rectangle extending to the right, and then pick out the 30% point for both draw and follow.

**from Jal** (from AZB post, which contains additional information):

When the balls are close enough to each other and/or you're hitting hard enough such that the cueball doesn't lose any significant backspin on the way to the object ball (or gain more topspin), there is a method of determining the cueball's direction once it reaches natural roll after the collision. I call it the Bottom-Center-Arrow method, or B-C-A for short, in that it's easy to remember.

Imagine a circle centered on the ghostball with the bottom of the circle running through the center of the cueball. This circle represents the face of the cueball from the shooter's perspective. To determine the CB's roll direction after the collision for any vertical offset (no sidespin applied), draw a line from the center of the real cueball parallel to the line of centers between the ghostball and the object ball. This will intersect the tangent line at 90°, call it point A. Thus, we have a triangle with the CB at vertex B (bottom of the circle), the ghostball at C (center of the circle) and point A from which we'll draw an arrow such that it intersects the vertical axis of the large circle. This yields the CB's direction once roll sets in, given that vertical tip offset on the face of cueball. Here's a diagram:... friction, amongst other things, has an effect on this idealized geometry.