# Viability of English and Low Squirt Shafts

#### Masayoshi

##### Fusenshou no Masa
Silver Member
I have to disagree here, if you have rolling CB at high speed and clean balls there will be no throw with english or no english. Just make sure the rolling already developed enough before it touches the OB.

Unless you have frictionless balls, you get throw on any cut shot no matter the speed. Sometimes the effects are miniscule, but they are still more than zero due to physics.

#### Masayoshi

##### Fusenshou no Masa
Silver Member
Dave:

Those are nice illustrations, but they're not proof of anything. They just illustrate your theory.

Whenever you mention "tip offset," I have to assume that you are meaning latitudinal offset. But I've been trying to emphasize that longitudinal tip offset plays a greater role than either latitudinal offset, or shaft "endmass," in the amount of actual cue ball deflection ("squirt") one experiences on any given shot.

My personal tests have shown that whenever I strike the cue ball above the equator with a normally elevated cue (which is more level than your illustration, by the way), using normal speed, and using parallel english (even though Patrick doesn't think parallel english exists), the cue ball rolls straight to the target. No deflection. No swerve. (At least that's what the observation from my end of the cue has always been.)

Last night, I had the opportunity to ask Tommy Kennedy to shoot this test multiple times while I observed the results from the other end of the table. Then I shot the test multiple times while he observed from the other end of the table. We both observed the same results: no deflection, no swerve. The cue ball did not push away from the aim line and then curve back to the aim line.

So, my assumption is that you must be hitting the cue ball lower than I whenever you do your tests; and my theory is that the different results are due to the difference in the amount of friction between the ball and the cloth. And, as long as you stay above the equator with your hit, it doesn't matter if you use a standard wood shaft, a graphite shaft, or a "low-deflection" shaft; the results will be the same: no deflection, no swerve.

Roger
(p.s. Tommy showed me some shots that can only be made with a graphite shaft, due to its stiffness. Just a little benefit to you Cue Tec users. :wink

Above center hits cause enough curve and throw to cancel out deflection at slow to medium speeds. Its extremely difficult to see with the naked eye (maybe impossible), but the cue ball is with out a doubt deflecting out and curving back in.

#### dr_dave

##### Instructional Author
Gold Member
Silver Member
Dave:

Those are nice illustrations, but they're not proof of anything. They just illustrate your theory.
Roger,

The diagrams are not based on my "theories." They are based on physics facts. And the physics facts can explain all observed effects.

Whenever you mention "tip offset," I have to assume that you are meaning latitudinal offset. But I've been trying to emphasize that longitudinal tip offset plays a greater role than either latitudinal offset, or shaft "endmass," in the amount of actual cue ball deflection ("squirt") one experiences on any given shot.
In the context of most of my squirt resources, "tip offset" refers to how far the tip contact point is from the center of the CB in the horizontal direction (left or right). I'm a bit confused by your use of "latitudinal" and "longitudinal" offset. To me, a latitudinal offset would imply a vertical tip offset since changes in latitude correspond to north/south motion. It seems like by "latitudinal" you meant moving across lines of latitude (in the longitudinal direction). Regardless, I think I know what you mean. However, let's use "left/right" and "up/down" to correspond to horizontal vs. vertical tip motion.

Getting back to the point, squirt (initial CB deflection) increases with both horizontal tip offset and with shaft endmass. Proof and video demonstrations of these facts can be found here:

Now, with most shots at a pool table, the cue isn't perfectly level, therefore the CB also swerves (after it squirts), which acts in the opposition direction as squirt. Here's a video demo clearly explaining and illustrating the different effects:

Now, as Jal has pointed out earlier (and as I think you are suggesting), there is less squirt when the tip contact point is above or below center. For more info, see:

However, with any shot where the tip is not on the vertical centerline of the CB, there will be squirt. There will also be swerve if the cue is not perfectly level (which is almost never the case at a pool table).

Now with topspin shots, the swerve happens very quickly, especially at slow speed. The amount of squirt can be very small (especially with a small amount of sidespin and a low-squirt cue), and the swerve can happen very quickly and cancel the squirt. In this case, it could appear like the CB is going in a straight line immediately off the tip. The squirt is too small to see over a short distance and the small amount of swerve happens too quickly to notice. However, the effects would become more noticeable with more sidespin and faster speed. Added cue elevation would also make the swerve effect more noticeable.

My personal tests have shown that whenever I strike the cue ball above the equator with a normally elevated cue (which is more level than your illustration, by the way), using normal speed, and using parallel english (even though Patrick doesn't think parallel english exists), the cue ball rolls straight to the target. No deflection. No swerve. (At least that's what the observation from my end of the cue has always been.)
I don't deny your results. Again, for a given amount of endmass, and for a given amount of sidespin, and for a given speed, the swerve can exactly cancel the squirt (i.e., there will be no net CB deflection from the aiming line), and the swerve can happen so quickly (e.g., over a couple of inches) that neither the squirt nor swerve would be noticeable.

So, my assumption is that you must be hitting the cue ball lower than I whenever you do your tests; and my theory is that the different results are due to the difference in the amount of friction between the ball and the cloth. And, as long as you stay above the equator with your hit, it doesn't matter if you use a standard wood shaft, a graphite shaft, or a "low-deflection" shaft; the results will be the same: no deflection, no swerve.
Results would definitely vary with amount of left/right tip offset (more squirt and more swerve), cue endmass (more squirt), shot speed (delayed swerve), cue elevation (more swerve), and cloth conditions (delayed swerve with slicker cloth).

It is very easy to demonstrate all of these real effects.

Regards,
Dave

#### Roger Long

##### Sonoran Cue Creations
Silver Member
Roger,

The diagrams are not based on my "theories." They are based on physics facts. And the physics facts can explain all observed effects.

In the context of most of my squirt resources, "tip offset" refers to how far the tip contact point is from the center of the CB in the horizontal direction (left or right). I'm a bit confused by your use of "latitudinal" and "longitudinal" offset. To me, a latitudinal offset would imply a vertical tip offset since changes in latitude correspond to north/south motion. It seems like by "latitudinal" you meant moving across lines of latitude (in the longitudinal direction). Regardless, I think I know what you mean. However, let's use "left/right" and "up/down" to correspond to horizontal vs. vertical tip motion.

Getting back to the point, squirt (initial CB deflection) increases with both horizontal tip offset and with shaft endmass. Proof and video demonstrations of these facts can be found here:

Now, with most shots at a pool table, the cue isn't perfectly level, therefore the CB also swerves (after it squirts), which acts in the opposition direction as squirt. Here's a video demo clearly explaining and illustrating the different effects:

Now, as Jal has pointed out earlier (and as I think you are suggesting), there is less squirt when the tip contact point is above or below center. For more info, see:

However, with any shot where the tip is not on the vertical centerline of the CB, there will be squirt. There will also be swerve if the cue is not perfectly level (which is almost never the case at a pool table).

Now with topspin shots, the swerve happens very quickly, especially at slow speed. The amount of squirt can be very small (especially with a small amount of sidespin and a low-squirt cue), and the swerve can happen very quickly and cancel the squirt. In this case, it could appear like the CB is going in a straight line immediately off the tip. The squirt is too small to see over a short distance and the small amount of swerve happens too quickly to notice. However, the effects would become more noticeable with more sidespin and faster speed. Added cue elevation would also make the swerve effect more noticeable.

I don't deny your results. Again, for a given amount of endmass, and for a given amount of sidespin, and for a given speed, the swerve can exactly cancel the squirt (i.e., there will be no net CB deflection from the aiming line), and the swerve can happen so quickly (e.g., over a couple of inches) that neither the squirt nor swerve would be noticeable.

Results would definitely vary with amount of left/right tip offset (more squirt and more swerve), cue endmass (more squirt), shot speed (delayed swerve), cue elevation (more swerve), and cloth conditions (delayed swerve with slicker cloth).

It is very easy to demonstrate all of these real effects.

Regards,
Dave

Dave:

I've viewed your video and read your resource pages on this subject numerous times, and I'm still not convinced that what you claim to be "physics facts" are are facts in all instances.

By your own admission, when you did your video tests you hit the cue ball with english on the horizontal center line. Plus, you hit it with considerably more speed and cue elevation than is required for most shots. Combining those three factors will definitely demonstrate what you wanted them to demonstrate: squirt and swerve.

But whenever I perform my tests, I hit with english above the horizontal center line. Plus, I use a normal speed (about 2-1/2 table length's travel) and a lower cue elevation. And when I perform the tests this way, neither my eyes, or Tommy Kennedy's eyes, have been able to detect any squirt or swerve.

Now I could use an illustration that would show the cue ball traveling in a straight line when I hit it in the above described manner, but that alone wouldn't prove that my findings are facts. But the same goes for your illustration. It's nice, but it doesn't really prove anything. It's just an illustration of what your training has taught you to believe are facts.

The real facts could only be proven if someone were to conduct robotic tests hitting the ball the way that I've been hitting it. Is that something you could do for us?

Roger

#### naji

##### AzB Silver Member
Silver Member
Dave:

I've viewed your video and read your resource pages on this subject numerous times, and I'm still not convinced that what you claim to be "physics facts" are are facts in all instances.

By your own admission, when you did your video tests you hit the cue ball with english on the horizontal center line. Plus, you hit it with considerably more speed and cue elevation than is required for most shots. Combining those three factors will definitely demonstrate what you wanted them to demonstrate: squirt and swerve.

But whenever I perform my tests, I hit with english above the horizontal center line. Plus, I use a normal speed (about 2-1/2 table length's travel) and a lower cue elevation. And when I perform the tests this way, neither my eyes, or Tommy Kennedy's eyes, have been able to detect any squirt or swerve.

Now I could use an illustration that would show the cue ball traveling in a straight line when I hit it in the above described manner, but that alone wouldn't prove that my findings are facts. But the same goes for your illustration. It's nice, but it doesn't really prove anything. It's just an illustration of what your training has taught you to believe are facts.

The real facts could only be proven if someone were to conduct robotic tests hitting the ball the way that I've been hitting it. Is that something you could do for us?

Roger

I notice one or two times Dr. Dave said you hardly can shoot a shot in pool with english unless you are elevated; i was going to answer but did not, now your post came. With high left or right or center and tip all the way at top you will have 100% leveled cue, and no need to adjust for swerve at all, maybe for slight squirt for very far shots, or CB close to a rail, or you shoot with pivot system.

#### dr_dave

##### Instructional Author
Gold Member
Silver Member
Dave:

I've viewed your video and read your resource pages on this subject numerous times, and I'm still not convinced that what you claim to be "physics facts" are are facts in all instances.

By your own admission, when you did your video tests you hit the cue ball with english on the horizontal center line. Plus, you hit it with considerably more speed and cue elevation than is required for most shots. Combining those three factors will definitely demonstrate what you wanted them to demonstrate: squirt and swerve.
Again, the purpose for the faster speeds and larger tip offsests was to clearly illustrate that the separate effects exist. And the changes in speed, sidespin, cue elevation, and endmass clearly illustrate how the effects change as predicted by the physics. The effects also exist at slower speeds and above-center hits with less sidespin, but they can be small and cancel each other out too quickly to notice them. The only way to demonstrate this, is to shoot with a range of speeds, vertical and horizontal tip offsets, cue elevations, and conditions to see how the effects change as predicted. FYI to you and others, all of the effect trends are summarized (with supporting resources) in the numbered list beneath the videos and illustrations here:
All of the trends have been verified with physics analysis, testing, and/or video demonstrations.

But whenever I perform my tests, I hit with english above the horizontal center line. Plus, I use a normal speed (about 2-1/2 table length's travel) and a lower cue elevation. And when I perform the tests this way, neither my eyes, or Tommy Kennedy's eyes, have been able to detect any squirt or swerve.
Again, I don't deny your results. You can't detect any squirt or swerve on these hits because the small amount of swerve is canceling the small amount of squirt too quickly to notice. What you are observing is no net CB deflection (i.e., no "squerve" or "effective squirt"). Again, I agree with you that the CB can appear to head very straight (and seem perfectly straight to the eye) with slow, near-level-cue, slow-roll shots with a relatively low-squirt cue.

The real facts could only be proven if someone were to conduct robotic tests hitting the ball the way that I've been hitting it. Is that something you could do for us?
I honestly don't see any need for such a test. You seem to agree that squirt and swerve exist, and you seem to be aware of how they change with shot speed, shaft endmass, amount and type of english, cue elevation, and conditions (as demonstrated in the videos). We also agree that squirt and swerve can be small and cancel with certain shots, so there is no net CB deflection. You just seem to disagree with the physics explanation for what you are seeing at the table for a specific type of shot. I don't think any experiment could convince you otherwise, nor is there a need to convince you. Results at the table are what really matter. You explain it one way (squirt and swerve don't exist for slow-roll shots with sidespin), and I explain it based on the physics that governs all shots with sidespin (for slow-roll shots with sidespin, with a near-level cue and a low-squirt shaft, squirt and swerve are small and cancel quickly), but we both agree on the outcome (the CB heads seemingly perfectly straight immediately off the tip).

Regards and Happy Holidays,
Dave

#### Roger Long

##### Sonoran Cue Creations
Silver Member
Again, I agree with you that the CB can appear to head very straight (and seem perfectly straight to the eye) with slow, near-level-cue, slow-roll shots with a relatively low-squirt cue.

You just seem to disagree with the physics explanation for what you are seeing at the table for a specific type of shot. I don't think any experiment could convince you otherwise, nor is there a need to convince you. Results at the table are what really matter. You explain it one way (squirt and swerve don't exist for slow-roll shots with sidespin), and I explain it based on the physics that governs all shots with sidespin (for slow-roll shots with sidespin, with a near-level cue and a low-squirt shaft, squirt and swerve are small and cancel quickly), but we both agree on the outcome (the CB heads seemingly perfectly straight immediately off the tip).

Regards and Happy Holidays,
Dave

Dave:

I'm getting my results with a standard shaft, so if you was to remove the terms "low-squirt cue" and "low-squirt shaft" from your explanations, we would be in perfect agreement. :thumbup:

Roger

#### AtLarge

##### AzB Gold Member
Gold Member
Silver Member
Roger -- Take a butt-screw joint protector that's flat on both ends, and put it on the center line of the table, with the CB resting in the pin hole, a bit off one of the short rails -- like teeing up a golf ball (a cube of chalk doesn't work as well). Strike the CB the way you describe ("above the equator with a normally elevated cue ..., using normal speed, and using parallel english").

Does the CB go straight down the center line of the table? No, it doesn't. It squirts out to the opposite side of the english and will probably strike the far short rail quite a distance from the center of the rail. Since the swerve effect is delayed while the CB is in the air, you are better able to see the squirt effect.

#### ENGLISH!

##### Banned
Silver Member
I understand the joint protector idea to give the CB squirt with no immediate swerve but the off line(squirt) could be caused by the CB rolling off of the curved edge of the joint protector. It might be 'better' to just get the CB to sit in the groove between the cushion & the rail & do the same thing.

Just trying to improve the parameters of the experiment.

Best Regards,

#### mantis99

##### AzB Silver Member
Silver Member
To be honest I don't think ld shafts make any appreciable difference in the production of spin, so I really think it just matters if you like the feel an ld shaft and want lower deflection. In my experience I can spin the CB the same with a regular shaft as with an ld shaft.

#### AtLarge

##### AzB Gold Member
Gold Member
Silver Member
... It might be 'better' to just get the CB to sit in the groove between the cushion & the rail & do the same thing. ...

On my table, a ball will not stay there, but it will stay on the cloth atop the cushion. I did try it from there, but I saw a more obvious effect of the squirt using a joint protector, perhaps because the cushion cloth had some effect doing it from the top of the cushion.

#### ENGLISH!

##### Banned
Silver Member
On my table, a ball will not stay there, but it will stay on the cloth atop the cushion. I did try it from there, but I saw a more obvious effect of the squirt using a joint protector, perhaps because the cushion cloth had some effect doing it from the top of the cushion.

That's interesting but makes some sense, I think. I was concerned that the squirt could be accentuated by rolling off of the curved edge of the joint protector. Coming off of the rail there could still be a bit of initial 'swerve roll' if hit softly enough.

In my experience, for all practicle purposes I would play the 10:45 or 1:15 location tip hits as Mr. Long suggests as though they had no squirt & allow for a bit of swerve depending on speed & cloth conditions.

As I have said several times in other threads, I had to sell a Predator 314 Cat shaft that had been 'juiced', sanded down. The reason was that on long shots with side spin, the CB started 'too straight' & the swerve spin took over & the ball rolled to fast & far to the english side. Dealing with that much swerve to squirt ratio differential was much more than I wanted to deal with after playing with regular 'deflection' shafts for nearly 46 years.

IMO LD shafts are very viable for using english but inhibit the shot where you 'throw'/deflect the CB out there & spin it back to gain more cut angle. Other than that shot, I have adjusted fine in about 2 months of just casual play after switching.

Best Regards,

#### EagleMan

##### Banned
I notice one or two times Dr. Dave said you hardly can shoot a shot in pool with english unless you are elevated; i was going to answer but did not, now your post came. With high left or right or center and tip all the way at top you will have 100% leveled cue, and no need to adjust for swerve at all, maybe for slight squirt for very far shots, or CB close to a rail, or you shoot with pivot system.

I used to believe exactly what you wrote above...but had it proven to me to be incorrect...at least on a Diamond table.

The shot was set up with the CB an inch off the head rail. A clip on level was placed on my cue to verify it was level.

I simply pushed the cue forward to contact the dead center of the virtical centerline with moderate speed...and I miscued 4 times in a row.

Admittedly, not all tables have the cushion profile of the Diamonds but I suggest that your "test" would only have a chance of success on rail profiles that are DEAD FLAT on top...and I don't think many of them are.

I suppose there are a FEW...a very few "normal" shots in pool where the butt of the cue doesn't pass over the rails and you could actually shoot UP toward the CB. But for all practical purposes very few shots in pool are actually level.

(-:

#### Patrick Johnson

##### Fish of the Day
Silver Member
naji:
I notice one or two times Dr. Dave said you hardly can shoot a shot in pool with english unless you are elevated; i was going to answer but did not, now your post came. With high left or right or center and tip all the way at top you will have 100% leveled cue, and no need to adjust for swerve at all, maybe for slight squirt for very far shots, or CB close to a rail, or you shoot with pivot system.
EagleMan:
I used to believe exactly what you wrote above...but had it proven to me to be incorrect...at least on a Diamond table.

The shot was set up with the CB an inch off the head rail. A clip on level was placed on my cue to verify it was level.

I simply pushed the cue forward to contact the dead center of the virtical centerline with moderate speed...and I miscued 4 times in a row.

Admittedly, not all tables have the cushion profile of the Diamonds but I suggest that your "test" would only have a chance of success on rail profiles that are DEAD FLAT on top...and I don't think many of them are.

I suppose there are a FEW...a very few "normal" shots in pool where the butt of the cue doesn't pass over the rails and you could actually shoot UP toward the CB. But for all practical purposes very few shots in pool are actually level.

(-:
EagleMan is correct about this, and even when you can get a perfectly level cue (those rare times when the butt isn't over the rail) swerve can be a factor, particularly with firmly hit shots. I believe it's because of "downward squirt" - the cue tip rolling up on the cue ball creates a downward force that combines with sidespin to produce some masse.

This swerve is the probable reason that naji (and others) believe there's little or no squirt when hitting above center on the CB.

pj
chgo

#### dr_dave

##### Instructional Author
Gold Member
Silver Member
... You can't detect any squirt or swerve on these hits because the small amount of swerve is canceling the small amount of squirt too quickly to notice. What you are observing is no net CB deflection (i.e., no "squerve" or "effective squirt"). Again, I agree with you that the CB can appear to head very straight (and seem perfectly straight to the eye) with slow, near-level-cue, slow-roll shots with a relatively low-squirt cue.
...
You seem to agree that squirt and swerve exist, and you seem to be aware of how they change with shot speed, shaft endmass, amount and type of english, cue elevation, and conditions (as demonstrated in the videos). We also agree that squirt and swerve can be small and cancel with certain shots, so there is no net CB deflection. You just seem to disagree with the physics explanation for what you are seeing at the table for a specific type of shot. I don't think any experiment could convince you otherwise, nor is there a need to convince you. Results at the table are what really matter. You explain it one way (squirt and swerve don't exist for slow-roll shots with sidespin), and I explain it based on the physics that governs all shots with sidespin (for slow-roll shots with sidespin, with a near-level cue and a low-squirt shaft, squirt and swerve are small and cancel quickly), but we both agree on the outcome (the CB heads seemingly perfectly straight immediately off the tip).
I'm getting my results with a standard shaft, so if you was to remove the terms "low-squirt cue" and "low-squirt shaft" from your explanations, we would be in perfect agreement. :thumbup:
I accept your friendly amendment. I'm glad we reached a description acceptable to both of us.

Now, if the shaft you are using results in no net CB deflection for your particular shot, a shaft with more endmass would result in a slight net deflection to one side (due to the extra squirt), and a shaft with less endmass would result in slight net deflection to the other side (due to the squirt being less than the swerve). Results would also vary with shot speed, cue elevation, and conditions.

Regards,
Dave

#### Jal

##### AzB Silver Member
Silver Member
EagleMan is correct about this, and even when you can get a perfectly level cue (those rare times when the butt isn't over the rail) swerve can be a factor, particularly with firmly hit shots. I believe it's because of "downward squirt" - the cue tip rolling up on the cue ball creates a downward force that combines with sidespin to produce some masse.
Patrick, that downward force doesn't produce any masse spin component. You do get downward squirt, but not a spin axis that is tilted forward or backward.

Jim

#### naji

##### AzB Silver Member
Silver Member
I used to believe exactly what you wrote above...but had it proven to me to be incorrect...at least on a Diamond table.

The shot was set up with the CB an inch off the head rail. A clip on level was placed on my cue to verify it was level.

I simply pushed the cue forward to contact the dead center of the virtical centerline with moderate speed...and I miscued 4 times in a row.

Admittedly, not all tables have the cushion profile of the Diamonds but I suggest that your "test" would only have a chance of success on rail profiles that are DEAD FLAT on top...and I don't think many of them are.

I suppose there are a FEW...a very few "normal" shots in pool where the butt of the cue doesn't pass over the rails and you could actually shoot UP toward the CB. But for all practical purposes very few shots in pool are actually level.

(-:

Thanks EagleMan, i use level cue all the time in one pocket going from one side to the other for soft shots. Maybe because my tip is 11 mm and can afford to bring it down 1 or 2 mm lower than a 13mm shaft and clear the table rail. At times i notice my stroke is not leveled and causes the cue to tilt while i am shooting to cause a little swerve, but i fixed that.

#### dr_dave

##### Instructional Author
Gold Member
Silver Member
EagleMan is correct about this, and even when you can get a perfectly level cue (those rare times when the butt isn't over the rail) swerve can be a factor, particularly with firmly hit shots. I believe it's because of "downward squirt" - the cue tip rolling up on the cue ball creates a downward force that combines with sidespin to produce some masse.

This swerve is the probable reason that naji (and others) believe there's little or no squirt when hitting above center on the CB.
Patrick, that downward force doesn't produce any masse spin component. You do get downward squirt, but not a spin axis that is tilted forward or backward.
Good point, Jim. The squirt direction is always in a plane through the center of the CB, because the cue tip deflects away from the center of the CB during contact as the spin is imparted.

The only way to get swerve is with a non-level cue, where the main impulse of the cue has a downward component (creating masse spin).

Regards,
Dave

#### chevybob20

##### AzB Silver Member
Silver Member
I'll try to keep this simple.

I believe in using english (meaning side-spin, only) whenever, and wherever, it is necessary in order to move the cue ball to a certain spot after it rebounds off a cushion. I also believe in using as much, or as little, english as is necessary to get the exact angle I need off of a cushion. I never use it to try and steer the cue ball before contact with the object ball unless I purposely employ a downward stroke with it.

I believe that cue ball deflection ("squirt") is something I have to deal with any time I hit the cue ball with english (meaning side-spin, only) on, or below, the horizontal axis with a firm stroke. I also believe that cue ball deflection is not something I have to deal with when I hit the cue ball with english (meaning side-spin, only) above the horizontal axis with a medium, or soft, stroke.

I believe that "low-deflection" shafts could lower the amount of cue ball deflection I might experience when hitting the cue ball with english (meaning side-spin, only) on, or below, the horizontal axis with a firm stroke; however, existing tests have shown that the actual amount of reduction achieved is not enough to entice me into paying a high price to acquire one, or interest me in spending any time to adjust to one.

I believe that robotic tests could be set up that would demonstrate my claims concerning the "above horizontal axis" hit. I also believe that all "low-deflection" shaft manufacturers would readily disagree with those same claims.

Roger

Roger has done this so long and responded so often that he may have created the most effecient low deflection shaft post in AZB history. Good post and thank you.

#### Patrick Johnson

##### Fish of the Day
Silver Member
Me:
...even when you can get a perfectly level cue (those rare times when the butt isn't over the rail) swerve can be a factor, particularly with firmly hit shots. I believe it's because of "downward squirt" - the cue tip rolling up on the cue ball creates a downward force that combines with sidespin to produce some masse.

This swerve is the probable reason that naji (and others) believe there's little or no squirt when hitting above center on the CB.
Jim:
Patrick, that downward force doesn't produce any masse spin component. You do get downward squirt, but not a spin axis that is tilted forward or backward.
Dave:
Good point, Jim. The squirt direction is always in a plane through the center of the CB, because the cue tip deflects away from the center of the CB during contact as the spin is imparted.

The only way to get swerve is with a non-level cue, where the main impulse of the cue has a downward component (creating masse spin).