Dr. Dave's answers to frequently-asked questions (FAQs), mostly from the AZB discussion forum
CTE aiming system
How does the Center-to-Edge (CTE) aiming system work?
CTE (Center-To-Edge) is an "align-and-pivot" pre-shot routine and "aiming system" that uses a line through the center of the CB and outside edge of the OB as a reference. There are several different versions and interpretations of CTE, but they are all based on establishing an initial "alignment" and then "pivoting" to the final aiming-line direction.
CTE Version 1 (an early and simplified "version" of CTE) - 3 pre-pivot alignments:
Here is a description of a version of the CTE, based on a video demonstration posted (and later removed) by eezbank, that he claimed was the version of CTE originally taught to him by Hal Houle:
For a "thick hit" (a small cut angle, less than about 15°) to the left:
- Align the cue 1 tip to the right of the CB center through the right edge of the OB.
- Place the bridge hand down with the cue along this line.
- Pivot the cue until the cue is pointed directly through the center of the CB.
- Stroke perfectly straight along this line.
For a "half-ball hit" (close to 30°) to the left:
- Align the cue through the center of the CB and through the right edge of the OB.
- Place the bridge hand down with the cue along this line.
- Stroke perfectly straight along this center-to-edge (CTE) line.
For a "thin hit " (a large cut angle, more than about 45°) to the left:
- Align the cue 1 tip to the left of the CB center through the right edge of the OB.
- Place the bridge hand down with the cue along this line.
- Pivot the cue until the cue is pointed directly through the center of the CB.
- Stroke perfectly straight along this line.
Here's a more-recent clarification from eezbank:
The way Hal teaches the system you pivot on every shot. So, the halfball info is wrong. Also, where I use the one tip reference Hal says it doesn't matter how many tips you use. You can start all the way to one side of the CB if that's what works with your pivot length.
CTE Version 2 (posted by Shawn Armstrong, as taught to him my Hal Houle) - 4 pre-pivot alignments:
The direction of the pivot, and the starting point, are determined by the angle of the cut. This is why you need to know the half ball hit angle. The alignment point on the object ball is always the outer edge. The starting point on the cueball is always the edge. However, it can be the inside or outside edge. That is determined by the cut angle.
For shots less than 30°, line up the center of the cueball with the edge of the object ball. Start with the outside edge of your cue tip lined up with the outside edge of the cueball. Pivot towards center. Your pivot should be leading you towards the center of the object ball.
For cuts greater than 30°, but less than 65, the pivot comes from the inside edge of the cueball. When you pivot to center, you should be going towards the outside edge of the object ball, away from the center.
For thin cuts, the pivots are edge to edge. For cuts between 65-80° (thicker than 80), the pivot is towards center from the outside edge of the cueball. For cuts thinner than 80, the pivot is from the inside edge of the cueball.
Thinner than 80, pivot from outside edge to center on the cueball, with the starting alignment being cutting edge of cueball to the cutting edge of the object ball. For razor cuts, line up outside edge to outside edge, and pivot away from the edge.
CTE Version 3 (posted by Dave Segal on Spidey's blog) - 2 pre-pivot alignments:
An excellent explanation and illustration of this approach, from mohrt, can be found here.
Note: CTEL = Center-to-Edge Line = line through CB center and perceived OB outer edge.
BASIC CTE PIVOTS (as taught by Hal Houle):
For thick cuts: Your cue is parallel to the CTEL with your tip pointing at the outside edge of the CB (the edge of the CB that’s farthest from the pocket). You then pivot your tip towards the pocket until it reaches CB center.
For thin cuts: Your cue is parallel to the CTEL with your tip pointing at the inside edge of the CB (the side of the CB that’s closest to the pocket). You then pivot your tip away from the pocket until it reaches CB center.
If you’re not sure which side to pivot from, only one will work. One will look right – the other will not.
For straight-ins: It doesn’t matter which side of the CB you address, just make sure you perform a thick-cut pivot.
Here's a more recent clarification from Spidey (based on a phone conversation):
What qualifies as a "thick cut" or "thin cut" isn't strictly based on the cut angle needed for a shot. It also depends on the distance between the CB and OB. You develop a sense for this as you work with the system.
CTE Version 4 (as interpreted by dr_dave from the description and examples on Stan Shuffett's Pro One DVD) - 6 pre-pivot alignments:
While standing, sight through the center of the CB and the outside edge of the OB (i.e., sight along the CTE line). Then, based on the type of cut (see the table below), shift your sighting to visualize a line through the inside edge of the CB to a given alignment point on the OB (see the table and figure below), while also maintaining the CTE visual. Then drop and slide into your stance straight toward the CB, placing your bridge to align the cue 1/2 tip off the CB's center (per the table and figure below). Now pivot the cue to the center of the CB with a fixed-bridge pivot. Here is a summary of the OB alignment points and pre-pivot tip positions for each type of cut:
cut type OB alignment cue tip alignment straight-in
inside 1/4* outside very thick cut
inside 1/4* inside medium thick
center outside medium
center inside medium thin**
outside 1/8 outside very thin**
outside 1/8 inside
inside: on the side of the ball toward the cut (i.e., the left side for a cut to the left, the right side for a cut to the right)
outside: on the side of the ball away from the cut (i.e., the right side for a cut to the left, the left side for a cut to the right)
*: If the CB-OB distance is less than about 1', sight to "inside 1/8" instead of "inside 1/4."
**: For thin cuts, you ignore the CTE visual and just sight for the 1/8-ball overlap.
You also need to adjust your bridge length for different CB-OB distances, based on the following table:
CB-OB distance > 2' about 2' about 1' < 1' very close bridge length 8-9" 7-8" 6-7" 5-6" very short
Note - Stan uses the "A," "B," and "C" notation (see the illustration above) to refer to the inside, center, or outside of the OB. With a cut to the left, the inside is "A" and the outside is "C." With a cut to the right, the inside is "C" and the outside is "A." "B" is always the center. For example, with a "very thick" cut to the right, you align the right (inside) edge of the CB with point "C" (inside 1/4). With a "very thick" cut to the left, you align the left (inside) edge of the CB with point "A" (inside 1/4). Also, Stan indicates the pre-pivot cue alignment based on whether the cue tip is "left" or "right" of center. For example, with a cut to the left, if the pre-pivot cue tip alignment is to the right (outside) of the CB center, Stan calls this a "right pivot." If the pre-pivot tip alignment is instead to the left of center ("inside" for a cut to the left, or "outside" for a cut to the right), Stan calls this a "left pivot."
You develop a feel for the alignments and pivots required for different shots based on practice and experience (i.e., there is no direct guidance on how to judge and choose the proper cut category for a given shot). You can also vary the cut angle created with a given CB-OB distance and a given alignment choice by varying your eye position some, also based on practice and experience.
Here are some example shot layouts and alignments (from Stan's first CTE Pro One DVD), originally posted by mohrt on AZB.
Here's a demonstration of how the pivots work.
from Stan Shuffett (from AZB post):
Previously, I added A and C as thin cut OB aimpoints. That was my first adjustment in 2 years to CTE PRO ONE.
After much study and consideration a FINAL adjustment in my CTE PRO ONE system is being implemented.
For shots at or near a zero angle and with CB and OB further apart than 1 diamond's distance, please note this change to your visuals.
Instead of using OBA or OBC as an aimpoint for the near zero angle shots, use CBE to OBE with a center to edge perception. All pivot information remains the same. Near zero angle shots can have slight left or right cuts.
This is my FINAL adjustment for any major system aspect of CTE PRO ONE.
from AtLarge (from AZB post):
After DVD1, Stan adjusted the visuals to include C (without a coupled CTE visual) for left cuts and A for right cuts, both with left or right pivots. So it would now be 8 instead of 6 in each direction.
[Although, ] A-left and B-right are now considered to produce the same result for left cuts.
CTE Evaluation and Analysis:
If you are good at judging the type of cut, version 4 above will generally work better than the others (without conscious or subconscious "adjustment") because it involves a larger number of pre-pivot alignments, which will offer better coverage over a wide range of cut angles (with a consistent pivot). Also, because there is less pivot than with the other versions, there will be less variation in results with different bridge lengths and CB-OB distances (see more info below).
If you follow any of the procedures above literally and exactly (without conscious or subconscious "adjustment" and with a consistent and non-variable pivot), you will make shots within certain limited ranges of cut angles and CB-OB distances for each resulting line of aim (see limited lines or alignments of aim). However, if you don't vary the alignment or pivot (see more below), you will miss shots outside of and between these ranges, unless the OB is close to the pocket or the pockets are large (providing a large margin for error). However, even if a person is not good at judging or "adjusting" between the alignments or by using a variable pivot, CTE still might be beneficial for any of the many possible reasons summarized here.
Many "challenges" relating to "aiming systems" are described and illustrated in "Fundamentals - Part III: DAM aiming system" (BD, November, 2008) and "Fundamentals - Part IV: bridge length" (BD, December, 2008). These difficulties certainly apply to CTE. Here's a good experiment you can use to test whether or not you understand how to apply CTE (or any pivot-based aiming method) effectively:
Shot "A" is about a 10° cut, shot "B" is about a 15° cut, and shot "C" is about a 20° cut. All three shots fit into the "thick cut" category of some versions of CTE. Also, the CB-to-OB distance is the same for all three shots. If the bridge length and pivot amount is the same for all three shots, a pertinent question is: What do you do differently with the alignment and/or pivot steps of CTE to pocket each of the three shots? There are several possible answers. You can:
1.) Change the initial alignment slightly (e.g., by shifting your eye alignment so the perceived cue alignment and/or parallel shift is different)
2.) Change the amount of the parallel shift (before the pivot) so you don't quite go all of the way to the perceived CB edge (e.g., shift a given number of "tips" instead)
3.) Pivot a slightly different amount (e.g., not quite to center, or just past center).
4.) Change the "effective pivot length" slightly (e.g., by adjusting your bridge length or by shifting/tilting your bridge during the pivot).
Options 1 and 4 are probably the most common approaches. The diagram below (from "Fundamentals - Part IV: bridge length" - BD, December, 2008) shows how a change in "effective pivot length" changes the amount of cut. The diagram shows two different bridge positions, but it could also represent two different "effective cue-pivot-points" created by a non-rigid-bridge pivot method (see more below).
If using a "mechanical pivot" (i.e., pivoting after placing the bridge hand down), one way to vary the "effective pivot length" is to vary the bridge length (as implied by the diagram). Another is to shift, rotate, tilt, or deform your bridge hand during the pivot as you shift your body (AKA "hip pivot"). Here are examples of this, posted by Colin Colenso, where the "effective pivot length" is changed with a bridge shift:
Another way is to use an "air pivot," where you pivot the cue and/or entire body before placing the bridge hand down. In this case, you can easily create any "effective pivot length" over an extremely wide range. Sometimes, the "effective pivot length" is referred to as the "shot arc." Here is a demonstration of how some forms of pivoting are used in conjunction with CTE and other pivot-based aiming methods: CTE pivot demonstration. For more info concerning pivoting, "air pivot," and "shot arc," see Spidey's blog.
The difficulty is in judging how much to change the initial alignment or "effective pivot length" to pocket balls requiring similar, but slightly different, amounts of cut. Many of the CTE proponents will say you don't need to know where the pocket is, or take into consideration the necessary amount of cut (other than to judge a "thin hit" vs. a "thick hit"), but this obviously cannot be the case. Maybe people who seem to use CTE effectively must at least sense where the pocket is (even if they don't look at it), or maybe they just have a feel for how much cut they need to pocket the ball. This sense or feel could influence their alignment or "pivot" in intangible ways that are difficult to describe or illustrate.
With all pivot-based aiming methods, the choice for "effective pivot length" must vary with the distance between the CB and OB, as illustrated by the following diagram from "Fundamentals - Part III: DAM aiming system" (BD, November, 2008). Note - the purpose for this diagram is simply to illustrate a general principle pertinent to all align-and-pivot systems like CTE and 90/90. The diagram is not meant to show a specific aiming example for any particular system or shot. The pre-pivot alignment shown is actually a 90/90 edge-to-edge (ETE) alignment, but again, this choice is not important for the point being made. With a fixed alignment (whatever alignment that might be) and a fixed "effective pivot length," the distance between the CB and OB has a huge effect on the resulting cut angle of the shot:
Interestingly, with the exact same initial alignment and pivot, two of the three balls can be potted if the pocket happens to be at points "a," "b," or "c." This would actually be a good proposition shot. Approach somebody who doubts pivot-based aiming systems and bet him or her you can make two radically different shots (e.g., shots "A" and "B" in the diagram) with the exact same initial alignment and the exact same pivot. You can even have the doubter shoot the shots for you, as long as his alignment and stroke skills are reasonably good. If the balls are lined up to take advantage of the effect shown in the diagram (i.e., if the balls are lined up so the corner pocket is at point "a" relative to the balls), both shots will go and you will win the bet.
The diagram above begs the following question: Is there a pivot length that would allow all three balls to be sent to the same position (e.g., where a pocket is located)? Unfortunately, this is not possible in this case. With a shorter pivot, the ball-hit fraction on shot "C" reaches 0 before all of the lines can meet:
and with a longer pivot, the CB aiming line will be closer to parallel to the the original alignment line, creating smaller cut angles, but the lines still can't all meet at one point:
and with a true parallel shift (infinite pivot length), all of the cut angles would be identical and the OB lines would be exactly parallel (i.e., they wouldn't intersect at all).
Here's another way to explain the impact of the limited lines of aim created by a limited number of initial alignments and pivot directions, applied again to the following three shots:
Instead of just the three shots (A, B, and C), consider 15 shots equally spaced between shots A and C. Let's use Stan's version of CTE for this example.
According to the system procedure, alignment and pivot choices change with shot cut angle. As the cut angle changes in small increments between shots A and C, the choices for alignment and pivot change at certain points in the range. For example, on Stan's DVD, he suggests an inside 1/8 OB alignment with with an inside cue tip position (for a left-to-right pivot) for shot "A," an inside 1/4 OB alignment (point A) with an inside cue tip position (for a 1/2-tip left-to-right pivot) for Shot "B," and a center OB alignment (point B) with an inside cue tip position (for a 1/2-tip left-to-right pivot) for Shot "C." At each point in the range of 15 shots where the alignment and/or pivots change, because neighboring shots of the group of 15 are so close together, different alignments and pivots would need to produce the same cut angle (e.g., to pocket the ball with an angle in between both choices). Also, the alignment and pivot will not change for certain ranges of shots within the 15. Therefore, a single alignment and pivot would need to create a range of cut angles. However, if you follow the procedure accurately and consistently for a selected alignment and pivot, with a given CB-OB distance and bridge length, assuming a rigid and fixed bridge, the procedure would result in the exact same cut angle every time (without conscious or subconscious "adjustments"). Obviously, this particular cut angle will work for some of the shots in the indicated range, and it won't work for others (depending on the distance to and size of the pocket), because every shot in the indicated range requires a different cut angle (assuming center-pocket aiming).
Now, does that mean you can't make CTE work for all shots at a table? Absolutely not. Four ways to make it work are summarized above. This is where "visual intelligence," "adjustment," "experience-based intuition," and "feel" come into play. And with enough practice, a person might be able to learn to apply one or more of the four techniques suggested, and do so naturally and even subconsciously ... to where they might not even know they are doing them.
Here's another useful experiment and drill related to Version 4 of CTE above:
1.) Place the CB on the head spot, and place the OB 2 feet in front of the CB on the table centerline.
2.) Ignoring the rails and pockets for now, cut the OB to the left using each of the alignments and pivots suggested by Stan's manual-pivot version of CTE, placing the CB and OB is the same positions for every shot. The six possible align/pivot choices for a cut to the left are:
from AtLarge (in AZB post): After DVD1, Stan adjusted the visuals to include C (without a coupled CTE visual) for left cuts and A for right cuts, both with left or right pivots. So it would now be 8 instead of 6 in each direction. But A-left and B-right are now considered to produce the same result for left cuts.
After each alignment and pivot, shoot the CB into the OB and note or mark the direction the OB heads on the table (maybe by marking where the OB hits the nearest cushion). Even though different people might see and execute the visuals, alignments, and pivots differently, a single person (if careful and consistent) should send the OB in a repeatable direction for each of the 6 choices (with a different angle resulting from each of the 6 shots). One can try these 6 shots multiple times to test and verify their consistency. This actually might be a good drill for dedicated CTE users out there.
3.) Now shoot the same shot again multiple times, this time sending the OB in a wide range of directions at and in between each of the 6 directions from step 2. If you desire, place a spare ball on the target cushion, and move it from one shot to the next, to simulate different pocket positions.
Alternatively, move the CB and OB together into different positions with the OB along an arc a fixed-distance from the corner pocket, always placing the CB 2 feet above the OB with the line through the ball centers parallel to the table centerline (and side rails). At each position, attempt to pot the OB in the corner pocket. Each of these shots will have the exact same CB-OB relationship and the exact same distance to the pocket. The only thing different will be the cut angle required to pocket the ball in the corner. Vary this angle, moving along the arc in both directions to cover the widest possible range of cut angles (from close to straight-in along the side rail adjacent to the corner, to the thinnest cut you can get with the balls close to the side rail across from the corner).
4.) For each angle or range of angles in step 3 (using either approach), explain the method used to decide which of the 6 align/pivot choices is used in each case. Also, for the directions that are between the 6 angles determined in step 2, clearly explain what is done differently during your pre-shot routine to create angles different from the original 6 directions.
This experiment is the easiest way to fully understand how CTE can actually work for the people who use it effectively over a wide range of shots.
BOTTOM LINE OF THE ANALYSIS : Any align-and-pivot system like CTE requires changes in alignment and/or effective pivot length as the cut angle and shot distance change.
DAM is still a much simpler approach to basic center-ball aiming than any pivot-based system; although, like anything, it does requires practice. Regardless of which "aiming system" you use (even if you just "see the angle"), you still need to practice to develop and improve your "visual intelligence" and consistency, and you need to actually focus on aiming the shot. It also helps to have an effective and consistent pre-shot routine. Many aiming systems can help some people do this (for more info, see benefits of "aiming systems"). Also, when you use sidespin, you need to compensate your aim to account for squirt, swerve, and throw.
insightful CTE-related quotes from others:
from mohrt (in AZB post), concerning step 4 of the final experiment suggested above:
mohrt: What you are doing "different" for every single shot is acquiring a unique visual for the given shot (which means a unique physical eye position for the given perception.) Many shots share the same alignment and pivot. But the perception is always unique. This is what leads to a unique connection for each and every shot line. As for determining when an alignment changes from one to the next, that comes from experience.
dr_dave: Based on your explanation, I would describe how CTE Pro One "actually works" like this: The pre-shot routine fostered by CTE Pro One creates a methodical framework that allows one to visualize and aim each shot more consistently and effectively. The alignments and pivots don't do the aiming for you. You still need to "acquire a unique visual" for a given shot and "perceive" the necessary line of aim on which you must place the fulcrum of your bridge (so the pivot brings you to the necessary line of aim for the shot).
from AtLarge (concerning Version 4 above):
If performed robotically, Stan's CTE is a discrete aiming method ("x-angle system" in pj's terms) rather than a continuous aiming method. That means, on paper, that it offers only a limited number of cut angles for any given distance between the CB and OB. If the CB-OB distance changes, you get another set of cut angles.
In use, however, I believe many players actually convert it into something more flexible (more cut angles) by slightly modifying something either before or after the pivot, based upon their knowledge of where the pocket is. I think those "feel" adjustments can become so routine and ingrained that the method starts to seem like a continuous method (unlimited cut angles at any CB-OB distance).
I'll say again what has been said many times about why it is an "x-angle" system. Let's say we're talking about cuts to the left. Stan's method calls for sighting the CB center to the OB right edge. That's the CTEL. Now, we have a secondary alignment line and a pivot direction to choose. But the menu offers only 6 choices for these: A with right pivot, A with left pivot, B with right pivot, B with left pivot, 1/8 to 1/8 with right pivot, and 1/8 to 1/8 with left pivot.
Assume the CB and OB are 3 feet apart. Place them anywhere on a flat surface. Forget about any pocket for now. Stan's method, if performed robotically for the two balls 3 feet apart, offers just 6 ways to align yourself, i.e., 6 ways to determine the final direction of aim of the cue stick. You could run through the entire menu of 6 ways to cut the OB to the left, replacing the two balls identically each time. You'll get 6 different lines of travel for the OB, i.e., 6 actual cut angles. Repeat the drill as many times as you want to with a 3-foot separation between the balls. You have only 6 menu items or 6 sets of instructions. If you do each of them the same way each time, you'll get the same cut angle each time for each of the 6 alignment-menu selections.
Now transfer the two balls to a pool table, but keep them 3 feet apart. You have the same 6 menu items or sets of instructions. If you perform them the same way, you should get the same 6 cut angles. But now, you have an intended pocket for the OB. This, at last, means you must choose just one of the 6 menu items for alignment. If you choose the best of the 6, and perform your alignment exactly as you did on the flat surface with no pockets, you should get the same cut angle that you did on the flat surface with no pockets. That actual cut angle may or may not be the cut angle necessary to pocket the shot. What increases the likelihood that the shot will be pocketed is that the player now knows precisely where the pocket is. His "visual intelligence," as some have called it, allows him to slightly modify something in his visuals, or in his stance, or in his approach to the table, or in his offset, or in his pivot, or ... in something. And that adjustment, be it conscious or subconscious, converts the 6-angle system into a more continuous system (far more cut angles for that 3-foot CB-OB distance).
from AtLarge (concerning Version 4 above):
dr_dave: For a given CB-OB relationship and cut direction, there is only one vertical plane or line through both the center of the CB and the outer edge of the OB (i.e., the CTEL), in 2D or 3D. If you are able to visualize more than one, that might explain how you are able to create a wide range of cut angles for a given CB-OB relationship (i.e., with the CB and OB a fixed distance apart).
AtLarge: Exactly, Dave. When users talk about the outermost edge or rotating edges, they must just be referring to viewing that plane, or a line in that plane, from a slightly different angle (i.e., the "vision center" isn't in that plane).
stan shuffett: If a player's eyes were positioned exactly the same for each shot, A and B, the results would be identical. ...[but]...The eyes are in different positions for each shot. ...Just because a CB and an OB share a common distance and the same visuals does not mean the eyes will be positioned the same way for each shot. Perception is altered with varied eye positions. ...
AtLarge: What is it, then, that guides the positioning of the eyes other than the CTEL and the secondary alignment line. I was under the impression that those two lines force an eye placement that "locks in" the two relevant edges of the CB and, therefore, control the pre-pivot cue alignment. The answer must have something to do with the actual pocket (target), right? Would you not call that something "visual intelligence" or "feel"?
stan shuffett: I would call it experience. Experience is our major teacher. ... I use the word experience as a reference to knowledge. ...
I take this input from Stan as revelatory. He is acknowledging that the basic set of prescriptions, if executed precisely the same way every time, would create only a small number of cut angles for a given CB-OB distance. So that issue should be settled. What, then, creates the additional cut angles; what turns a discrete method into a continuous method -- one with enough cut angles to pocket all shots? Where is the "feel" being introduced? Stan has now answered that question -- it is different eye positions for the same set of visuals. In other words, for any particular shot and alignment-menu choice, such as this:CB-OB distance = 3 feetmultiple cut angles can be achieved by viewing the CTEL and secondary alignment line from different eye positions.
cut to left
secondary alignment line to "B"
bridge length = 8"
cue offset = 1/2 tip
pivot from left to right
How does one know where to put his eyes? It is knowledge gained from experience. Stan did not acknowledge that this is "feel," but I'm sure many of us would view it that way, as feel in any aiming method is developed from experience in using the method.
So there we have it. Stan's manual CTE depends upon utilizing multiple eye positions within each of the basic 6 alignments. The feel or additional knowledge is not introduced by varying the offset, or by varying the bridge length (beyond what Stan prescribes), or by fudging the pivot -- it comes from knowing where to place the eyes while still somehow holding to the underlying pair of visuals for each of the prescriptions.
I hope this really puts an end to the squabbles. Manual CTE is not some voodoo hocus pocus. It is not geometric magic. There are no supernatural powers to align-&-pivot methods. It doesn't work because of numerology -- the table being 1x2 or 90 being the sum of 45, 30, and 15. It works by utilizing a small number of reference alignments that the player has learned to fine tune based on his explicit knowledge of where the pocket is and the appearance of the cut angle needed for the shot, i.e., his experience-based knowledge of the shot needed.
dr_dave: I would add to your synopsis that CTE can also provide many other potential benefits to some of its users.
from Patrick Johnson (concerning Version 3 above):
First, what I think it is: I think CTE is a "reference" aiming system (very similar in concept to, and in fact an outgrowth of, Hal Houle's old "3-angle" system), that divides all the possible shots into two categories (thinner or fuller than half ball), leaving the final aim adjustment up to you to learn "by feel". I think it adds some suggested "systematic" adjustments, but nobody can seem to describe those, which makes me think they're probably mostly learned by feel too.
How it works/what it offers: I think CTE offers its users the following things:
1. A specific and easy-to-see starting place (the half-ball alignment) that's in the middle of all the possible alignments. Each shot can be "measured" in relation to the half-ball alignment, giving some structure to an otherwise wide-open (and maybe daunting) narrowing-down process. (This is also the way the old 3-angle system worked, but with three reference angles rather than just one.)
2. A specific and easy-to-see starting alignment of the stick, CB and OB (again, the half-ball alignment) that brings your focused attention to how those three things are aligned, something very helpful in learning to aim (and in executing aim once you've learned it) but often overlooked.
3. Because of its structured approach to aiming, a confidence boost that helps your mind make focused "recordings" of successful shot alignments which can be more readily recalled for future similar shots ("learning by feel").
These might not be all the benefits (see Dr. Dave's website for a list that may go beyond these). I don't believe any of these benefits are only available from CTE, but CTE may be the best way to get them for some players.
The controversy surrounding CTE is about whether or not it's an "exact" system that doesn't rely on the player's ability to finish the aiming process "by feel". Since nobody can seem to describe the whole process (actually, nobody can seem to clearly describe any of it past the initial half-ball alignment), it seems obvious to some (including me) that it therefore can't really be an "exact" system and must include some (maybe a lot of) feel. For some reason, CTE users can't stand this idea and argue vehemently against it (this may be part of the confidence thing), but their arguments always boil down to the same thing: it works for them.
I take CTE users' word for the fact that "it works for them" and only take issue with the claim that it doesn't involve any "feel", but the arguments usually become unfocused very quickly and devolve to "it works" vs. "it can't work", giving us all lots of opportunities for playing the dozens (trading clever insults), but shedding no light whatsoever.
from SpiderWebComm (Dave Segal) (concerning Version 3 above):
- You should never sight directly down the CTEL (center to edge line). Your head should always be on one side or the other. I like pretending the CTEL is a vertical plane ... my body leans against it, one side or the other.
- The bridge position is not really correct in the diagram... it's never on the CTEL. I did it this way just for simplicity in making the diagram. My only intent is to show how the shot circle works - not the other details of CTE.
Consider the following:
What you see here applies to any shot until the distance between the OB and CB is less than the bridge length. I always shorten my bridge to a distance short than that between the CB and OB when this happens. Technically, a "pivot" isn't required at all - that's another story... you can step into the top of the shot circle from one side of the CTEL.
If you were to rotate the cue in the bridge as a true pivot (once again, pretend a nail is driven through the point where the cue touches the skin and into the slate), the cue would turn around the bridge circle radius. This is why people miss shots completely. You would technically only turn the cue like this on a short shot.
For the "mechanical pivoters" out there, you always place your bridge first. Once you're set in your bridge, the cue is turned along the shot circle arc, in relation to the OB - not "rotated/pivoted" from the bridge (bridge circle arc).
This is just a helpful way to describe what is really happening. This is not a functional way of playing....i.e. no one has to "see" a circle on the table in order to make any shot. This is really a "classroom" style of learning how to pivot (um, turn your cue).
OK - practical application when at the table: You should see the OB as a two-dimensional object on a vertical plane (think of the OB as a sticker on a window when down on your shot). Imagine your cue extending to the window and scrape your tip along it until you hit center ball. That's what I do. I only "see a shot circle" on very close shots - within, say, a foot or so.
Notice the longer the shot is, the bigger the circle--- the flatter the arc (think of the Earth - when you look at the horizon, it's nearly flat). The shorter the shot, the smaller the circle--- the curvier the arc (think of a basketball).
I think the reason why so many people say this is a visual system is because they "pivot to the OB" and make the shot and don't know why.
In conclusion, the "correct" center of the CB is determined by the position of the OB, always.... not by the bridge position/bridge length.
from Colin Colenso (concerning Version 3 above):
Any cue that moves or turns from one position to another can be described as having been pivoted at some distinct point. On CTE shots this pivot point must be behind the CB and usually it is behind the bridge hand so the shape of an arc, projected to the front of the shot circle would always be flatter than the actual shot circle arc.
Hence, it seems more like the shot circle is an approximate visualization method, like, as you've said, scraping your tip along a distant window. This is fine, but it's not very quantifiable or systematic, other than it would seem to indicate that you can intuitively sense the nature of the turn and that the turn pivots noticeably closer to the CB with closer distance shots.
Regarding edges of the OB, technically there is only one edge each side that is on the CTE line, but I understand that one's perception of variations in this edge change if one sights the various angled shots from different positions relative to the CTE line.
from Jal (concerning Version 3 above):
[The dependence on pivot length] is why it's not an exact system and why a majority of shots will be missed unless some intuitive adjustment is made. However you have the stick aligned prior to pivoting, the correct pivot point is on a line from the center of the ghostball through the center of the cueball. Where that line crosses the long axis of the cue, is the place to pivot.
Of course, if you can picture where the ghostball is located with sufficient accuracy to make the shot, on the face of it, there seems to be little point in doing the pre-alignment/pivoting procedure. That's related to the main bone of contention between those who are critical of these types of systems, and those who support them: unless you can come up with some procedure for determining the pivot distance that's not tied to shot geometry (impossible), the system(s) are not exact and rely on the experience and judgment of the player to make the final crucial adjustment, consciously or subconsciously.
That's not to deny that many have found them useful.
[Here's a list of many reasons why some people find CTE and other aiming system useful.]
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