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

for more information, see Section 7.01 in The Illustrated Principles of Pool and Billiards and

and Disc II of How to Aim Pool Shots (HAPS)

*How are combination shots (combos) aimed?*

The following video from Disc II of How to Aim Pool Shots (HAPS), covers the basics:

Generally, the easiest way to aim combos is to simply apply whatever aiming system you use ... twice. One technique is the ghost-ball cue-pivot method demonstrated in the following videos:

NV 7.1 - Aiming a combination shot

NV D.9 - How to Aim Pool Shots - from Vol-II of the Billiard University instructional DVD series

You first place the cue tip at the necessary ghost-ball position for the 2nd OB. Then pivot the cue to visualize the necessary line of aim for the 1st OB. Then place the tip at the required ghost-ball position to send the 1st OB along this line. Pivoting the cue to the CB then gives the necessary line of aim for the shot.

Aim must also be compensate for throw, especially with slow-speed small-gap or frozen combinations. For more information see "HAPS - Part V: Combination-Shot Throw" (BD, March, 2015) and the following videos:

NV E.5 - Combination Shot Throw Adjustment, from HAPS II

NV J.1 - Small-Gap-Combination Throw Effects and Game-Situation Examples

NV D.17 - Does a pool and billiards frozen combination throw more than a small-gap stun shot?

NV J.1 - Small-Gap-Combination Throw Effects and Game-Situation Examples

For more information, see frozen-ball throw and small-gap combos.

*How do you aim combination shots when the gap between the balls is small?*

The following video explores throw effects related to small-gap combinations with various gap sizes between the balls:

Here are some useful conclusions from a math/physics analysis in TP B.21:

- When the gap between the OBs is 3/8" (9.5mm), the 2nd ball heads very straight (i.e., the throw effect cancels the cut effect) over a fairly wide range of 1st-ball angles, regardless of ball conditions. At larger angles, the 2nd ball heads in the cut direction (because the cut effect is larger than the throw effect). Fortunately, 9.5mm is just slightly smaller than the diameter of typical low-CB-deflections shafts, so it is easy to judge the optimal gap size with your tip. Alternatively, you can visualize the gap size as 1/3 the radius of a ball (1/3 * 1.125" = 1/3 * 9/8" = 3/8"). Alternatively, visualize 3/8" as between 1/4" and 1/2" (which many people can picture fairly easily).
- When the gap between the OBs is very small (much less than 3/8" or 9.5 mm), the 2nd OB heads in the throw direction at smaller 1st-ball angles and slower speeds (except at really small angles where speed has no effect), but the 2nd OB heads in the cut direction at larger angles and faster speed. The largest throw effect occurs close to a 1/2-ball hit.
- When the gap between the OBs is larger than 3/8", the 2nd OB always heads in the cut direction, regardless of shot speed; although, throw reduces the cut more at slower speed (except at small angles where the speed has no effect).
- When the gap between the OBs is 1/4" (6 mm), a fast speed shot results in less accuracy for small angles (less than about 15 degrees), but the accuracy is within +/- 1 degree over a larger range of 1st-ball angles. For 1st-ball angles below about 20 degrees, the error is in the throw direction, and for angle above about 20 degrees, the error is in the cut direction.
- If a small-gap combo is wired to the center of a pocket, with a gap size between 1/4" (6 mm, about 1/2 the width of a typical shaft) and 1/2" (13 mm, about the width of a typical shaft), anything fuller than a 3/4-ball hit between the 1st and 2nd OB will result in pocketing the 2nd ball (at any speed) for average distances and pocket sizes.

When there is no gap between the balls, the 2nd ball throws the most (but not much more than when there is a very small gap). For more info and demonstrations, see the frozen-ball throw resource page.

The info above also applies to cut shots where the CB is close to the OB and hit with stun. The difference is you have direct control over the CB's spin. With small-gap cuts, sidespin can be used to change the throw amount and/or direction, and top/bottom spin will reduce the amount of throw (see throw draw/follow effects).