If you’ve been paying any attention at all over the last couple of months, you’re likely already aware of the recent USBC rule modifications affecting how bowling balls can be drilled. Just to recap, here are the relevant changes1:
- Balance holes will become illegal effective August 1, 2020. If you have any bowling balls with balance holes that you wish to use in USBC-sanctioned competition on or after that date, you must have the balance hole plugged.
- Starting August 1, 2018, balls that do not have balance holes (including balls with balance holes that have been plugged) are allowed to have up to ±3 ounces of static imbalance in all directions (side, finger/thumb, and top/bottom).
- From August 1, 2018 until July 31, 2020, balls that do have balance holes are limited to the “old” static imbalance rules of ±1 ounce for side weight, ±1 ounce for finger/thumb weight, and ±3 ounces for top/bottom weight.
The bottom line with these rule changes is that there is essentially a two-year “phasing in” period that gives bowlers time to adjust to the new rules. If you so desire, you can start drilling balls right now that conform to the new rules (no balance holes, but with looser static imbalance limits). Or, for the time being, you can continue drilling balls that conform to the old rules (with balance holes, but with the old, stricter static imbalance limits). Also, bowlers now have the option to start plugging their balance holes in preparation for the August 1, 2020 balance hole ban. You certainly don’t have to do this right away—you have almost two years before balance holes officially become illegal—but it is certainly an option for people who want to start moving their arsenals in the direction of the future rules.
In my last article, I addressed the topic of static imbalance in quite a bit of detail. If you haven’t yet read it, I encourage you to do so now, as much of that article is relevant to what follows. In this article, I’ll focus on the other piece of the puzzle: balance holes. We have a lot of ground to cover, so let’s get right to it.
First of all, don’t panic!
If you read my last two articles (here and here), then you already know that I’m very much not a fan of the balance hole elimination rule change. I think it’s quite pointless, and I believe that it will prove to be completely ineffective in producing the outcomes outlined by the USBC2.
In most cases, for balls that already have balance holes, plugging them isn’t going to make much of a difference in terms of on-lane performance. And, when you go to drill your next new ball, the fact that you can’t use a balance hole just isn’t going to significantly change the maximum amount of performance you can get out of it.
We’ll talk more about all of this in detail below, but the bottom line for concerned bowlers is that there isn’t much to panic about when it comes to this new rule change. In short, don’t worry: your ball will probably still hook without a balance hole.
But how can I say all this? Didn’t the USBC just do three years of research that proved balance holes are a problem that needs to be fixed? Didn’t they just prove that eliminating balance holes will reduce the hook of bowling balls by two boards?
In my opinion, no and no.
I’ve read every last word of the USBC’s recently-published research3 on this topic—over 100 pages of information—and they simply don’t make a compelling case in support of their narrative that eliminating balance holes will “help maintain the playing environment by reducing overall hook by approximately two boards4.”
I simply don’t believe that a traditional flare-increasing balance hole (such as a P3 or P4 hole, to use the terminology of the popular Gradient Line Balance Hole system5) creates a significant increase in hook in an already-high-flaring bowling ball. This is actually fairly straightforward to test and demonstrate. Brunswick did it more than 10 years ago6. Storm published a test that showed this just a few weeks ago7. And, I’ve done this kind of test myself—numerous times—both in the real world and in the world of physics-based ball motion simulations. The result is always the same: adding a traditional flare-increasing balance hole to an already-high-flaring bowling ball does not make it hook significantly more, all other things equal.
But, this is not to say that balance holes—in general—do nothing to the performance of bowling balls. That’s not what I’m saying at all. In some cases, balance holes do make balls hook significantly more than they did without the hole. And, in some other cases, balance holes do make balls hook significantly less than they did without the hole. But, in a lot of situations, they just don’t have as significant an effect as many bowlers seem to believe.
Let’s look at the theory behind this—along with some examples—so that you can gain a better understanding of what to expect as you transition into life after balance holes over the next several years.
Basic balance hole theory
Most everything you need to know to understand balance holes and their impact on ball performance has already been covered in my previous article on this topic. In case you don’t feel like re-reading it, here’s a brief recap8.
Balance holes can no doubt have a strong effect on the mass properties of the bowling ball, and that can no doubt have a strong effect on how much track flare the ball has. But, the extent to which those things affect the ball’s on-lane motion varies quite a bit. In other words, in some cases, a giant flare-increasing balance hole will make a ball hook significantly more. But, in other cases, that same giant flare-increasing balance hole might make it hook slightly less. This might sound confusing, but—as I said in my earlier article on this topic—not all identical balance holes are created equal. To put it another way, not all identical balance holes create the same effect on the ball’s motion.
One important key to understanding balance holes is to understand the very non-linear relationship between track flare and on-lane performance. “On-lane performance” is a vague term, of course. But, to keep things simple, let’s think of this term as primarily meaning total hook. Track flare affects total hook approximately as shown below.
To summarize the above graph, total hook increases as track flare increases, but a point of diminishing returns is eventually reached at which point additional track flare results in ever-diminishing amounts of additional hook. On the left portion of the above graph, each of the ball track’s oil rings overlaps the previous one by some amount. This overlapping of adjacent oil rings reduces the amount of friction the ball experiences. As track flare increases (moving to the right on the graph), the flare rings widen, resulting in less oil ring overlap and more exposure of fresh ball surface to the lane, which results in increased friction. But, at some point, the flare rings become fully separated, and further separation begins to have a very diminishing effect on the amount of friction the ball creates.
What this means is that one of the keys to understanding how a balance hole will affect your ball’s motion is to consider where the ball is on this track flare spectrum prior to adding the hole, and where it will be on this spectrum after adding the hole. We’ll look at a handful of examples of this below, in the context of balance hole plugging.
But, before we do that, it is important to mention that track flare isn’t the only thing influenced by a balance hole that affects the ball’s motion. There are also the effects that the balance hole has on the ball’s RGs, its static imbalance, and its overall mass. In most cases, these effects all tend to be fairly small from a ball motion standpoint, whereas the effect of differences in track flare can either be very large or very small, depending on the situation.
Balance hole plugging examples
Let’s look at a few examples of what happens when various types of balance holes are plugged. As per the usual for me, these examples will be done using a bowling ball drilling and on-lane motion simulation software tool that I’ve been designing, developing, and validating for the better part of the last decade.
I hope these examples will give you an improved understanding of what to expect as you prepare your equipment for the 2020 balance hole ban.
We’ll start with a fairly typical scenario—one that might look a lot like some of the balls in many of your bags today. Put simply, this is a high-flare ball and layout that use a flare-increasing balance hole.
Since this ball uses a flare-increasing balance hole, we would expect the ball’s differentials to go down upon plugging the hole. And, that’s exactly what happens, as the plugged-hole ball shown below has 0.009″ less total differential than it did with the balance hole drilled.
But, plugging this ball’s balance hole does not make it hook less, as many of you might have expected. In fact, the plugged-hole ball will hook just a tiny bit more than the non-plugged ball.
Why does this happen? Well, let’s analyze it. With the balance hole, this ball flared approximately 9 inches in total (which includes the amount it flared on the dry back end). After we plugged the hole, it flared noticeably less—about 8 inches—but that’s still quite a large amount of track flare.
When you take a ball from 9 inches of track flare (which is a lot) down to 8 inches of track flare (which is also a lot), there is almost no reduction in the amount of friction the ball is able to create with the lane. Why? The ball’s fully-separated flare rings still remain fully separated. There will be a tiny bit of friction reduction as the ball track enters and exits the bowtie regions (where the oil rings cross), but this represents a small percentage of the ball track, and hence has a small impact. The net result is that a flare reduction from 9 inches to 8 inches is going to do almost nothing to reduce the amount of friction the ball encounters.
That explains why the plugged-hole ball didn’t hook less. But, we haven’t yet explained why it actually hooked slightly more after plugging. The answer to this was alluded to in both my last article on static imbalance and in my earlier article on balance holes: plugging the balance hole alters the ball’s static imbalance in such a way as to cause it to hook slightly more. Specifically, the addition of side weight and top weight in the plugged-hole ball make it hook a tiny bit more and generate a tiny bit more angle on the back end than it did prior to plugging. But, keep in mind that we’re talking about small changes to the ball’s motion—about half an inch of hook in this case, which isn’t enough for most bowlers to ever even notice.
At a high level, the takeaway here is simple: for situations similar to the one described above, plugging the balance hole isn’t going to make a huge difference in the overall reaction of the ball.
Now let’s look at another common situation: a high-flare ball and layout that use a flare-decreasing balance hole. This would typically involve a balance hole over near the bowler’s positive axis point (PAP), in the P1 or P2 location.
Since this was a flare-decreasing balance hole, we should expect that plugging it will increase the ball’s total differential. And, that’s exactly what happens, as the plugging of the hole increases the differential by about 0.005″.
But, again, plugging this ball’s balance hole has almost no noticeable impact on its performance. In this example, the plugged-hole ball will hook ever-so-slightly more than the pre-plugged ball.
The reasons here are pretty much the same as in the previous example: this ball flared a very large amount both with the hole (6.6 inches) and with the hole plugged (7.7 inches), resulting in almost identical amounts of friction with the lane.
And, just like in the previous example, plugging the balance hole changed the ball’s static imbalance in such a way as to make it hook slightly more.
While the last two examples showed very little impact on ball motion from plugging the balance holes, that won’t always be the case. Another somewhat common scenario is that of a low-flare ball that ends up getting a flare-increasing balance hole added to it in order to make it hook more. The example below shows a lower differential ball that uses a pin-down layout, a 5.5 inch pin-to-PAP distance, and a large flare-increasing balance hole.
Plugging this ball’s balance hole will weaken its dynamics considerably. Specifically, its differential drops by about 0.008″ and its as-drilled high RG axis moves by about 2 inches from its fairly strong position 4.67 inches from the PAP to a very weak position 6.60 inches from the PAP.
So, given these changes to its mass properties, we most certainly would expect this ball to flare less with its balance hole plugged. It certainly does (see below), but, in this case—unlike Example #1 above—this reduction in track flare causes a significant reduction in total hook.
To understand why, let’s return to our total hook versus track flare graph again. Before this ball’s hole was plugged, it flared about 3.5 inches, which is a moderate amount of track flare. Plugging its flare-increasing balance hole reduced its flare rather significantly, down to about 1.5 inches, which is very little.
In this case, the ball with the plugged balance hole is flaring so little that it is creating significantly less friction with the lane than it did when it had the hole. This causes the plugged-hole ball to hook significantly less than it did prior to plugging the hole. Also, just like in the first two examples, this example’s plugged-hole ball has static imbalances that create slightly more hook than the non-plugged ball. But, in this case, the overwhelmingly dominant factor is the effect of the change in track flare.
Now, there’s something related to this particular example (really, all of these examples) that I’ve seen and heard a lot over the last few months that I want to draw some attention to. A lot of people seem to be under the impression that when you drill a large, deep balance hole into a ball, you dramatically reshape the ball’s core, and that when you subsequently plug the balance hole, the ball will still maintain a lot of what the hole provided (in this case, increased total differential, increased intermediate differential, and a stronger as-drilled high RG axis location relative to the PAP) even after it is plugged. In other words—in the context of this example—the common belief is that even after plugging this ball’s balance hole, it will still remain strong because of how the balance hole reshaped the ball’s dense core, only to then be filled in with comparatively lower density ball plug material.
In most cases, this simply isn’t true. I’m sure there are some exceptions, but, in general, plugging the balance hole returns the ball to almost exactly the same mass properties that it had prior to drilling the balance hole to begin with. I covered this in quite a bit of detail in a previous article on the effect of plugging and redrilling9, but let’s look at how this plays out for this specific scenario.
Prior to adding the balance hole, the ball’s mass properties are as shown below.
We already showed the mass properties both after adding the balance hole and after plugging the balance hole (see images above). A summary of the key mass properties that relate to the ball’s track flare potential is shown below.
So, as I hope you can clearly see, even though the very large balance hole used in this scenario did “reshape” the core, the ball ended up with almost the exact same mass properties after drilling the hole and then plugging the hole as it had prior to drilling the hole to begin with. This should be good news for the people out there who think that a ball with a plugged balance hole is somehow ruined or somehow inferior. That is completely false. A ball with a plugged balance hole will almost certainly be almost exactly the same—at least from a mass properties standpoint—as an otherwise-identical ball that never had a balance hole to begin with.
Getting back on track, what do you do if the ball in this example is your ball? You probably drilled it the way you drilled it on purpose, in order to produce a certain ball motion. And now, after you plug the balance hole, you end up with a completely different motion. What can you do in this situation?
Unfortunately, not much. One possible option might be a full plug and redrill using a higher-flaring layout. This would be somewhat costly, and a lot of bowlers just wouldn’t want to deal with this headache. Another possible option is to see if the plugged-hole ball now somehow fits into a different place in your arsenal. For example, now that the plugged-hole ball in this example flares very little, perhaps you could put some surface on it and use it on fresh shorter oil patterns (as an alternative to urethane, for example). The final option is that you might decide to just retire this ball completely and start over with something new. None of these options are great, but the good news is that most of us don’t have very many bowling balls in our arsenals that will require such drastic measures.
We’ve covered some of the more common scenarios above with our first three examples. Let’s look now at a couple of more specialized cases.
While most balance holes are either of the flare-increasing, flare-neutral, or very slightly flare-decreasing variety, it is also possible—although far less common—for a ball to have a balance hole that significantly decreases its flare potential. Below is an example, which shows an Ebonite Game Breaker 2 with a large balance hole drilled into the bottom of its core that dramatically reduces its differential and track flare potential.
When this balance hole is plugged, the differential of the ball is strengthened significantly, from 0.020″ up to 0.033″.
The result of this increase in differential is rather drastic when the ball is thrown. With the hole plugged, it hooks about 4 boards more than it did with the hole.
I think the reason for this increase in hook should be obvious by now for most of you. But, in case it isn’t, let’s return again to our hook versus flare graph:
As you can see, prior to plugging the balance hole, this ball flared very little—only about 1.8 inches in total. After plugging the hole, it flared quite a bit more—about 4.5 inches. This drastic increase in flare caused the ball to experience more friction with the lane, which created more hook.
So, what is the owner of this ball to do? Well, the owner of this ball is actually me, so I’ll share my thoughts. This ball was drilled for a specific purpose, and it has served that purpose very well for the last several years. When thrown with a lot of surface, this ball starts hooking very early and then has a very slow and gradual hook phase. It is great as a first ball out of the bag for me on shorter and medium length sport patterns. After plugging its balance hole, it certainly won’t be able to serve its original purpose anymore, as it will respond to friction much more quickly. I’ll likely need to buy a new ball—one that has a much lower total differential, drilled with a differential-lowering pin-down layout—to fill this void in my arsenal.
But, truth be told, I probably won’t be in much of a hurry to get this ball plugged. I suppose that’s one positive about the way the balance hole ban is being introduced: over the next two years, it’s completely up to the bowler when they choose to have their balance holes plugged.
We talked about what are typically thought of as traditional balance holes in Examples #1, #2, and #3, and then we talked about a specific type of not-so-traditional balance hole in Example #4. There is one more type of balance hole that is worth a mention here, and that is the flare-increasing hole placed on the bottom of the ball, approximately 180 degrees from what we typically think of as the P4 location.
My first experience with this type of balance hole came in 2011, when my very reluctant pro shop operator agreed to drill my new ball’s very strange balance hole, and then watched with me in shock as it performed exactly as my computer had predicted. Balance holes like this on the bottom of the ball got a little bit of attention in a 2012 issue of Pro Shop Operator magazine10 in an article about non-traditional layouts, but this type of thing really gained widespread popularity in 2013, when Mo Pinel’s variation—known as the “MOtion Hole”—came onto the scene11.
The significance of this type of balance hole is that it can actually increase the performance—in terms of both total hook and entry angle—of balls that are already flaring a large amount. In other words, this type of hole can take an already-strong ball and make it stronger—at least for certain styles of bowlers. Buy why? Why does this type of balance hole—which is essentially on the other end of the same axis upon which you’d place a P4 hole, and which essentially changes the ball’s RGs and differentials identically to a P4 hole—make the ball so much stronger?
The magic of this kind of balance hole is that it causes the ball to continue to hook after it reaches the roll phase. The reason? Top weight. This concept was covered in detail in my last article, but when a ball flares significantly, its axis of rotation migrates from the release PAP—which is typically on the side of the ball—to somewhere closer to the “top” of the ball—through or within a few inches of the grip center and beyond. This puts the CG—and the “heavy side” of a ball that has a lot of top weight—on the left side of the ball on the back end (for righthanders). This imbalance causes the ball to hook, even after it loses all of its axis rotation angle and starts to roll without slipping.
Let’s take a look at an example of what happens when this type of balance hole gets plugged. We’ll start with a high differential ball, using a high-flaring pin-up layout and a large balance hole drilled near the “negative” end of the ball’s high RG axis.
Plugging this balance hole changes the ball’s mass properties as shown below:
The plugged-hole ball has significantly lower total and intermediate differentials, which will definitely make it flare less. Also note that it has significantly less top weight. This translates into ball motion differences as follows:
As shown above, the plugged-hole ball hooked less. But, in this case, the reduction in hook had very little to do with the ball’s reduction in track flare. As you can see below, it flared quite a lot both with the balance hole drilled and with the balance hole plugged (it’s very similar to Example #1 in this way):
The difference in hook and performance is primarily the result of changes to the ball’s static imbalance. When the hole was plugged, mass was added to the bottom of the ball, which reduced its as-drilled top weight. This makes the ball reach the roll phase earlier, with less total hook, and with less angle change on the back end.
If you happen to be a bowler who likes to use balance holes like this, what are your options after the August 1, 2020 balance hole ban? Well, obviously, you won’t be able to achieve this type of motion anymore through the use of balance holes, but that doesn’t mean it will be completely impossible to create. Remember, the motion created by this type of hole is mostly the result of a static imbalance trick—namely, having a lot of top weight in the drilled ball. So, if you want to see similar motion in a ball without a balance hole, you just have to get the drilled ball as close as possible to 3 ounces of top weight—and use a ball and layout that flare enough to make top weight have an effect downlane. All of this can still be done without a balance hole, but you’ll need to start with a ball that has a lot of top weight to begin with.
The big caveat—as mentioned in my last article—is whether or not high top weight balls (in the 4+ ounce range) will become readily available in the future. You can’t do what I described above with a ball that has 2 to 3 ounces of undrilled top weight, and that’s what is what is typically available nowadays.
Considerations when drilling new balls
So far, we’ve talked about what to expect when plugging your existing balance holes. We still need to talk about what to expect when you drill new balls under the new rules.
If I were to sum things up as briefly as possible (which isn’t exactly a strength of mine), I’d say the following about drilling new balls under the new rules:
- We’ll have a bit more freedom in what kind of layouts we can use, because we won’t have to worry so much about keeping the CG where it needs to be to meet the old ±1 ounce limits for finger/thumb weight and side weight.
- We’ll have way less freedom in how we can alter our balls’ motion after drilling, because we will no longer have the option to add a balance hole.
Related to this first point, think about something basic like a low-end plastic ball, just for illustration purposes. These balls typically have very low differentials (pancakes, small pucks, etc.), with the CG designed to coincide with the low RG axis. Some of the older urethane and present-day entry-level reactive balls also fit this description.
Traditionally speaking, balls like this are usually drilled with the CG very close to the center of the grip, which tends to reduce the already-low differential and results in very little track flare. This will no longer be a requirement under the new rules. Now, for example, a plastic ball (or an entry-level reactive ball with a pancake-style weight block) can be drilled with layouts that put the CG/pin in much higher-flaring positions. Whereas these type of balls traditionally only flared a tiny bit in the past, new layouts will be possible that will make them flare quite a bit going forward:
In balls with higher differential cores, the impact will be far less severe—after all, we already have lots of layouts for these type balls that make them flare and hook a ton. But, one positive side effect is that we won’t be as limited in the kind of layouts we can use in a given ball. For example, it used to be somewhat important to look at the pin-out distance (the distance from the pin to the CG) when selecting a ball: if you know, for example, that you want to drill the ball with the pin way above the fingers (a pin-up layout), you’d likely want to make sure you started with a long pin-to-CG distance ball (4 inches or more, for example). This will matter far less under the new static imbalance rules, as pin-up layouts will now be possible with shorter pin-to-CG distance balls, since it won’t be so hard now to stay under the maximum finger weight limit.
My second point above—having less freedom in how we can alter our balls’ performance after drilling—is one that is sure to irritate bowlers and pro shop operators alike. It has become a fairly common practice in recent years among better ball drillers to plan ahead when selecting layouts in order to provide for the option of adding a balance hole, if requested by the customer after they’ve had a chance to see how a given ball performs. This will unfortunately be a thing of the past in the very near future. We’ll still have surface adjustments as a way of tweaking ball motion in an already-drilled ball, but it’s a shame that we’ll be losing such an easy way of changing the ball’s dynamics after drilling.
In light of everything discussed in both this article andin my previous article on static imbalance, I think that a decent piece of advice for most bowlers is to just carry on with laying out and drilling your new balls in mostly the same ways you always have. Of course, the adventurous and curious bowlers among us should feel free to take what was presented in these two articles and experiment however much they like. Just don’t expect that things will be radically different under the new rules: the bowler, the lane conditions, and the ball’s coverstock will still be the dominant factors in ball motion going forward. The new rules do provide for the possibility of different types of layout trickery for certain situations—and especially for very low rev rate, low ball speed bowlers, as outlined in my last article. But, by and large, most of us as bowlers just aren’t going to feel much of an impact in our everyday bowling lives.
So what happens next? We’re still very much at the beginning of this new era of drilling rules, so the future is still a bit uncertain—at least from my vantage point.
It will be interesting to see how—and to what extent—the bowling ball manufacturers react to the recent drilling rule changes. It seems likely that we’ll eventually see some new core designs, some updated layout recommendations, and possibly some reconfiguration of their product lines (in terms of things like core/coverstock pairings, differential levels, number of symmetrical vs. asymmetrical balls, etc.). And, as I mentioned in my last article, it remains to be seen if anyone will start manufacturing and marketing higher top weight bowling balls than what we typically see today.
I expect that we’ll also start to hear more about various types of “inventive” drilling schemes: thumb holes that are 8 inches deep, giant balance holes that are strategically drilled and plugged to alter the ball’s core, etc. These sort of things are fine as long as no rules are being broken, but most of this “creative” stuff really won’t be all that necessary in most situations.
In closing, I really hope that the information shared in my last two articles helps you better understand how the USBC’s recent drilling rule “enhancements” might affect your game going forward. While I’m definitely not a fan of these changes, the bottom line is that most of us as bowlers will be minimally impacted, and that life goes on.
1. United States Bowling Congress. “USBC adjusts timeline for new bowling ball specifications.” bowl.com. https://www.bowl.com/News/NewsDetails.aspx?id=23622331380 (accessed August 29, 2018).
2. United States Bowling Congress. “Frequently Asked Questions: Bowling Technology Updates.” PDF file, 3. http://usbcongress.http.internapcdn.net/usbcongress/bowl/equipandspecs/pdfs/TechnologyStudy/2018BTS-FAQ.pdf (accessed August 29, 2018).
3. United States Bowling Congress. “Bowling Technology Study – Conclusion.” bowl.com. https://www.bowl.com/BowlingTechnologyStudy/ (accessed August 29, 2018).
4. United States Bowling Congress. “Frequently Asked Questions: Bowling Technology Updates.” PDF file, 3. http://usbcongress.http.internapcdn.net/usbcongress/bowl/equipandspecs/pdfs/TechnologyStudy/2018BTS-FAQ.pdf (accessed August 29, 2018).
5. MoRich Bowling Ball Co, LLC. “Gradient Line Balance Hole.” PDF file. http://wiki.bowlingchat.net/wiki/images/c/c6/GradientLine.pdf (accessed August 29, 2018).
6. Brunswick. “USBC’s Proposed X-Hole Ban.” YouTube video, posted by Eric Morrett. https://youtu.be/f1e8VeZf4WA (accessed August 29, 2018).
7. Storm Bowling. “New USBC Rules – Balance Holes and Performance.” YouTube video, posted by Storm Bowling. https://youtu.be/d9zahj7etws (accessed August 29, 2018).
8. Sempsrott, Bill. “Bowling Ball Balance Hole Fundamentals.” Bowling This Month. https://www.bowlingthismonth.com/bowling-tips/bowling-ball-balance-hole-fundamentals/ (accessed August 29, 2018).
9. Sempsrott, Bill. “The Effect of Plugging and Redrilling on Bowling Ball Mass Properties.” Bowling This Month. https://www.bowlingthismonth.com/bowling-tips/the-effect-of-plugging-and-redrilling-on-bowling-ball-mass-properties/ (accessed August 29, 2018).
10. Bergendorf, Dennis. “Look Out for These Layouts.” Pro Shop Operator. Issue 3, 2012. 10-12. Print.
11. “MOtion Hole – How To & Demonstration.” YouTube video, posted by Eric Morrett. https://youtu.be/I05-Sqe-MCo (accessed August 29, 2018).