The Fog Break • Equipment • Essay
The Physics of Putting

What Your Putter Actually Does—and Doesn’t Do—at Impact

A forensic look at the physics of blade, mallet, and zero-torque designs. The math doesn’t care about marketing.


There is a quiet crisis of honesty in the putter industry. Every new release promises better roll, more forgiveness, and a straighter path to the hole. The claims are rarely wrong in a strict sense—they’re just incomplete in ways that matter. When you understand the physics of what happens during the half-millisecond a putter face touches a golf ball, the picture becomes both simpler and more humbling than any product launch would suggest.

This is an attempt to lay it out plainly. Not which putter is “best,” but what each design philosophy is actually correcting for, what it trades away, and why the unsexy truth—that your stroke mechanics matter more than any piece of equipment—keeps surviving every wave of innovation.

• • •

The Half-Millisecond That Decides Everything

Impact lasts roughly 500 microseconds. During that window, the putter head behaves as a free body—the shaft has essentially no influence because the forces are too large and the duration too short for vibrations to travel up and back.1,2 Everything that matters is determined by the state of the clubhead at the instant of contact: its velocity, its orientation, and where on the face the ball makes contact.

Research across multiple studies and measurement systems converges on a stark hierarchy. Somewhere between 83% and 92% of the ball’s starting direction is determined by the face angle at impact.3,4,5 The remaining 8–17% comes from the path of the putter head. This isn’t an opinion or a manufacturer’s claim. It falls directly out of oblique impact mechanics—at putting speeds, friction between the ball and face is high enough that the ball essentially launches perpendicular to whatever the face is doing at the moment of contact.6

The practical consequence is severe. At eight feet, a face angle error of just one degree means a miss. At fifteen feet, half a degree. At thirty feet, you need the face square to within two-tenths of a degree—the angular width of roughly three sheets of paper held at arm’s length.

Maximum Allowable Face Angle Error for a Center-Line Putt
DistanceMax ErrorContext
3 feet2.04°The “gimme” range. Still demands precision.
5 feet1.22°Tour make-percentage drops sharply here.
8 feet0.76°One degree open = miss.
15 feet0.41°Half a degree. Sub-conscious control territory.
30 feet0.20°Effectively impossible to guarantee.
THE GEOMETRY OF A MISS Angles exaggerated ~10× for visibility 0.76° OPEN SQUARE 1.28" OUTSIDE THE CUP 8 FEET 0.76°Max face error at 8 ft 83–92%Direction from face angle MISSAt just 0.76° open
Fig. 1 — The Geometric Reality. At eight feet, less than one degree of face angle error at impact sends the ball entirely outside the cup.

→ Try this interactively: adjust face angle, distance, and putter type

Every putter design, no matter how novel, has to be evaluated against this table. The question is always: does this design help the golfer deliver the face within these tolerances more consistently? And if so, at what cost?

• • •

The Blade: Simplicity, Feedback, and the Price of Both

A traditional blade putter—a Ping Anser, a Scotty Cameron Newport, a Bettinardi BB-series—is the simplest expression of the physics. Most of the mass sits in a compact head near the face plane. The center of gravity is shallow (close to the face) and the moment of inertia is relatively low, typically 2,500 to 4,500 g-cm².

What the blade does well

Because the CG sits close to the face, blades have a critical advantage that rarely makes the marketing copy: minimal gear effect on off-center hits. When you miss the sweet spot, the head rotates around its center of gravity. If that CG is close to the face, the rotation produces very little tangential velocity at the contact point, so the ball still launches close to the face-normal direction. Research using adjustable-CG putters showed that a 15mm toe strike launched only 0.23° offline with a shallow CG design versus 0.59° with a deep CG—even though the deep CG putter had 20% higher MOI.7

That number deserves emphasis. The putter with more forgiveness on paper sent the ball more offline in practice, because the directional error from gear effect overwhelmed the speed preservation from higher MOI. Putts starting 0.23° and 0.59° offline miss the hole at 47 and 18 feet, respectively.

CG DEPTH AND THE GEAR EFFECT Top-down view — same 15mm toe strike on both putters BLADE CG Rotation Force 0.23° offline — misses hole beyond 47 ft Shallow CG creates a mostly horizontal lever. Rotation pulls face straight backward, so ball launches nearly straight. MALLET CG Rotation Force Pushed Offline 0.59° offline — misses hole beyond 18 ft Deep CG creates a diagonal lever. Rotation creates sideways friction, kicking the ball sideways. The mallet had 20% higher MOI. It sent the ball 2.6× more offline. More “forgiveness” on paper. Worse directional accuracy in practice. Source: Lambeth et al. — adjustable CG/MOI putter, robotic testing
Fig. 2 — The Mallet Tax. Both putters struck 15mm toward the toe. The blade’s shallow CG creates a mostly horizontal lever, pulling the toe straight backward on rotation. The mallet’s deep CG creates a diagonal lever, so the face slices sideways across the ball, kicking it offline via gear effect — despite having 20% more MOI.

Blades also provide clearer sensory feedback. The lower MOI means off-center strikes feel distinctly different—there’s more twist, more vibration, a different sound. This isn’t a flaw. For a player developing their stroke, that honest feedback is a calibration signal. You know immediately when you’ve missed the center, and your motor system can adapt.

What the blade demands

The flip side is unforgiving. That same low MOI means off-center hits lose significant energy. In robotic testing, a traditional Anser-style putter twisted six times as much as a high-MOI design on a half-inch mishit, and the impact ratio (ball speed divided by putter speed) dropped from 1.70 to 1.52—enough to leave a putt about three feet short. The high-MOI putter barely budged, from 1.70 to 1.69.8

WHAT HAPPENS ON A ½-INCH MISHIT Robotic test — center hit vs. ½" off-center LOW MOI (BLADE) ~3,000 g·cm² TWIST 6× baseline SPEED 1.70 → 1.52 ≈ 3 FEET SHORT HIGH MOI (MALLET) ~8,000+ g·cm² TWIST 1× baseline SPEED 1.70 → 1.69 ≈ 2 INCHES SHORT Same mishit. The blade leaves you 3 feet short. The mallet leaves you 2 inches short. Source: Quintic Ball Roll Lab — robotic putter testing
Fig. 3 — The Distance Forgiveness Case for MOI. On a half-inch off-center hit, the low-MOI blade loses enough energy to leave a putt three feet short. The high-MOI mallet barely notices. This is the one variable where the mallet advantage is unambiguous — but it only addresses distance, not direction.

A blade also typically has toe hang, meaning the toe naturally drops when you balance the shaft on your finger. This introduces gravitational torque during the stroke—the head wants to rotate open on the backswing and closed on the downswing. This isn’t a defect; it’s a feature if your stroke has a consistent arc. The natural rotation of the head matches the natural arc of a shoulder-pivot stroke. But if your arc varies from putt to putt, the putter’s built-in rotation becomes one more variable you have to time correctly.

A blade putter is an honest instrument. It rewards precision and punishes inconsistency with equal clarity. The question is whether you want your putter to tell you the truth or to cover for your mistakes.

The blade golfer

If you have a consistent, repeatable arc stroke with good center-face contact, a blade gives you the most directionally accurate launch off the face—especially on mishits—because of that shallow CG. The feedback loop is tight and honest. Tour professionals, who strike the ball within an eighth of an inch of center consistently, derive maximum benefit from this design. For higher-handicap golfers whose strike pattern spans an inch and a half across the face, a blade is actively punishing their misses on distance control while offering a directional advantage they may not be consistent enough to exploit.

• • •

The Mallet: Forgiveness and Its Hidden Tax

Mallet putters—TaylorMade Spiders, Odyssey 2-Balls, Ping Tyne-series designs—distribute mass across a larger footprint, pushing weight to the perimeter and corners. This dramatically increases MOI, typically to 4,500–7,000 g-cm² and in extreme cases beyond 10,000. The physics case for this is straightforward and real: higher MOI means less twist on off-center hits, which means more consistent ball speed.

What the mallet does well

Distance control on mishits. Full stop. This is the one variable where mallets deliver a measurable, physics-backed advantage that scales with handicap. The worse your strike consistency, the more a high-MOI design helps you. A golfer whose contact point wanders three-quarters of an inch from center—which is conservative for a mid-handicapper—will see dramatically tighter distance dispersion with a 6,000 g-cm² mallet versus a 3,000 g-cm² blade.

Most mallets are also face-balanced or near face-balanced, meaning the face points skyward when you balance the shaft. This reduces the gravitational torque during the stroke, which in principle means less timing demand on face rotation. For a golfer with a straighter, less arced stroke—particularly one driven by the shoulders with minimal wrist involvement—this is a genuine mechanical match.

The hidden tax: CG depth and gear effect

Here is the trade-off that almost no fitting session and no marketing brochure will explain to you. To get all that mass distributed around a large perimeter, the center of gravity moves deeper—farther behind the face. And CG depth is the primary driver of horizontal gear effect.

When you strike the ball toward the toe, the head rotates around its CG. A deep CG means the face moves through a larger arc at the contact point during impact, imparting a tangential kick to the ball. The result is the ball launching farther offline than the face angle alone would predict. You gained distance forgiveness but paid for it in directional accuracy.

This is the central design tension in modern putters, and it’s real: MOI and CG depth are geometrically linked. You cannot push mass to the perimeter of a large footprint without pushing the centroid backward. Some manufacturers have attempted to break this coupling with face-forward CG designs, lightweight body materials with dense face inserts, or variable-depth milling to normalize ball speed without needing perimeter weighting. These are legitimate engineering solutions to a real physics problem, but they’re complex trade-offs, not free lunches.

The irony of the modern mallet is that the feature making it “more forgiving” on distance simultaneously makes it less forgiving on direction—the variable that matters five times more.

The mallet golfer

If your primary putting problem is distance control—three-putts from lag range, inconsistent pace, wide contact dispersion—a high-MOI mallet genuinely helps. If your primary problem is direction on mid-range putts, the deep CG might be working against you. The ideal mallet player has a relatively straight stroke, doesn’t need the putter to rotate with their arc, and benefits more from tighter speed than from the last tenth of a degree on launch direction. This often describes the mid-to-high handicapper, but not always.

• • •

Zero Torque: Attacking the Right Problem a New Way

Lie angle balanced putters—L.A.B. Golf being the originator, with Odyssey, Evnroll, PXG, Scotty Cameron, and others now offering versions—represent the most interesting design divergence in decades. They attack a different variable entirely: not what happens during the 500-microsecond impact, but what happens in the thousand milliseconds before it.

The physics problem they solve

Every traditional putter has its center of gravity offset from the shaft axis when the club is held at its playing lie angle. This offset creates a gravitational torque—the head wants to twist in one direction when you hold it naturally. In toe-hang designs, the toe drops. In face-balanced designs, the face points up only when the shaft is horizontal, not at the 70° lie angle where you actually putt.

WHY TRADITIONAL PUTTERS TWIST Front-on view — what happens when you let the putter hang naturally TRADITIONAL PUTTER HEEL TOE CG LEVER ARM GRAVITY pulls CG down FACE TWISTS Offset CG creates a lever arm. Gravity acts on lever, forcing rotation. LIE ANGLE BALANCED HEEL TOE CG CG mapped directly to shaft axis GRAVITY pulls through axis FACE STAYS SQUARE Lever arm is zero. Torque is zero. Face naturally remains stable at rest.
Fig. 4 — The Torque Problem. When you hold a traditional putter at its lie angle, gravity pulls the offset CG downward. Because the CG sits away from the shaft, it creates a lever arm, generating torque that twists the face open. Lie angle balanced designs align the CG precisely with the shaft axis, reducing the lever arm (and therefore gravitational torque) to zero.

Lie angle balanced putters align the CG with the shaft axis at the lie angle. This zeros out the gravitational torque component. The face has no inherent tendency to rotate open or closed during the stroke. You swing it back, you swing it through, and the face stays perpendicular to the arc without you fighting anything.

Given that face angle determines 83–92% of starting direction, and given that the golfer’s job is to deliver the face within fractions of a degree, eliminating one source of unwanted rotation is a defensible physics decision.

What zero torque doesn’t solve

This is where the honest conversation gets harder. Zeroing gravitational torque is not the same as zeroing all torque. The putting stroke creates dynamic forces—centripetal acceleration, tangential acceleration through the arc—and these interact with the putter’s inertia tensor to produce cross-coupled rotations even in a perfectly balanced design. The putter is a non-symmetric rigid body; its products of inertia don’t vanish just because you’ve balanced it at rest.

Additionally, a lie-angle-balanced putter doesn’t address contact point, it doesn’t change the CG-depth/MOI trade-off, and it doesn’t alter the oblique impact physics at the moment of contact. If you deliver the face one degree open with a zero-torque putter, the ball still launches one degree open—it just might be easier to avoid that scenario in the first place.

There’s also a subtler issue. Some golfers have grooved a stroke that relies on the putter’s natural torque profile. A player with an arced stroke and a toe-hang blade has, over thousands of putts, calibrated their timing to the putter’s rotation. Remove that rotation and the calibration is gone. The putter is objectively more stable, but the golfer’s muscle memory is now mismatched. This isn’t a flaw in the technology; it’s a transition cost. But it’s real, and it’s why some excellent putters try a zero-torque design and putt worse for weeks before they adapt—or decide the old feel was more trustworthy.

The zero-torque golfer

If you struggle with face control—pushes, pulls, inconsistent starting lines particularly under pressure—a lie-angle-balanced putter removes one mechanical variable from the equation. Golfers who tend to grip tightly or whose wrist action varies under stress may benefit the most, because the putter is no longer amplifying those micro-inconsistencies. But the golfer who already has excellent face control and relies on feel and timing may find the reduced feedback unsettling. The technology is sound; the question is whether it matches your error pattern.

• • •

Face Milling and Inserts: The Most Oversold Variable

This is where the gap between marketing and physics is widest, and it’s worth being direct about it.

The claim: grooves, deep milling patterns, and polymer inserts generate topspin, reduce skid, and produce a “truer roll.” The research: face treatments change the coefficient of restitution and the friction characteristics of the impact, but controlled studies have found that they do not get the ball into pure rolling earlier for a given putt length.9 A putted ball enters true roll after approximately 20% of its total distance regardless of face treatment.10

Why? Because what governs the transition from skid to roll is primarily dynamic loft at impact and the vertical position of the CG relative to the strike point—not the surface texture.9 A putter delivered with two degrees of loft striking the ball slightly above the CG projection will produce forward rotation via vertical gear effect.11 A putter delivered with four degrees of dynamic loft and a low strike will produce backspin regardless of how aggressively the face is milled.

What face treatments actually do

Two things that are real and one that’s psychologically important:

First, variable-depth milling can normalize ball speed across the face. By making the face softer (deeper grooves, lower COR) in the center and firmer toward the edges, the energy penalty for a mishit is reduced. This is conceptually similar to what high MOI does for twist, but operating through a different mechanism—contact compliance rather than rotational inertia. It’s legitimate engineering.

Second, face texture affects the coefficient of friction during the 500-microsecond contact. Higher friction means the ball is more likely to grip the face (stick regime rather than slide regime), which pushes the face-angle-to-launch-direction ratio even higher toward 90%+. In principle, this makes the face angle even more dominant and the path even less relevant. Whether this is “good” depends entirely on whether your face angle is more reliable than your path.

Third—the psychological dimension—grooves and milling alter the sound and vibration profile at impact. Deep milling reduces the contact area, dampens higher frequencies, and produces a softer, more muted sensation. Many golfers associate this with “purity.” That feeling of confidence is not nothing. Believing you’ve made solid contact frees mental bandwidth for the next putt. But it’s a perceptual benefit, not a ballistic one.

No face milling pattern can fix a face that’s one degree open at impact. The ball doesn’t care what the grooves look like. It cares where the face is pointing.
• • •

The Irreducible Problem: It’s Still Your Stroke

Here is the uncomfortable truth that survives every generation of putter innovation.

Your putting stroke is a coupled oscillator. The primary motion—the putter swinging back and through in the sagittal plane—is driven by a shoulder pivot and behaves roughly like a pendulum. Research shows that consistent putting comes from driving this system near its natural resonant frequency, which is what golfers experience as “rhythm” and “tempo.”12

But face angle control happens in a second, perpendicular plane—rotation around the shaft axis. And this secondary motion is coupled to the primary stroke through the putter’s inertial properties.13 As you accelerate the putter through the ball, centripetal and tangential forces act through the offset CG and produce torques that try to rotate the face. Your neuromuscular system must counteract these varying torques with precisely timed hand and wrist inputs to deliver the face square at the exact instant of contact.

THE STROKE AS A COUPLED SYSTEM Two motions happen simultaneously — and they interfere with each other PRIMARY MOTION Back and through — the pendulum PIVOT Back IMPACT Through Controls: SPEED + TEMPO Driven at natural resonant frequency COUPLED Stroke forces disturb face angle SECONDARY MOTION Face rotation — opening and closing SHAFT OPEN SQUARE CLOSED < 1° window Opening IMPACT Closing Controls: DIRECTION (83–92%) Must be timed to < 1° at impact Every putter design is a different strategy for managing this coupling. None eliminate it.
Fig. 5 — Two Motions, One Moment of Truth. The primary pendulum motion (left) controls speed and tempo. The secondary face rotation (right) controls direction. The two are coupled: accelerating the putter through the ball creates forces that try to twist the face. The golfer must arrive within a sub-1° window at the exact instant of impact. Every putter design manages this coupling differently. None eliminate it.

Different putter designs manage this coupling differently. High MOI makes the face respond more sluggishly to disturbing torques. Lie angle balance removes the gravitational torque component. Toe hang matches the putter’s natural rotation to an arced stroke. But none of these eliminate the fundamental challenge: the stroke creates torques, and the golfer must time their response to within fractions of a degree at the exact moment of impact.

This is why putting statistics on tour don’t correlate neatly with equipment. Great putters are great because their motor control system can reliably deliver the face within the tolerances the geometry demands, putt after putt, under pressure, on varying surfaces. The putter they use is the one that best matches their particular stroke mechanics and error tendencies—not the one with the highest MOI, the most exotic face milling, or the latest torque-elimination technology.

• • •

The Dimple in the Room

One final piece of physics that should give every equipment obsessive pause. A golf ball is not a sphere. It is a dimpled approximation of one, and those dimples introduce irreducible randomness into every putt.

When the flat putter face contacts the curved surface of a dimpled ball, the contact may fall on the edge of a dimple rather than on the smooth land between dimples. This can deflect the launch direction by up to roughly one degree—an amount that exceeds the allowable error window for any putt longer than about four feet.14,15 This isn’t theoretical. Physics experiments have shown that golf balls don’t roll in straight lines even on perfectly flat, horizontal surfaces.16 Each dimple introduces a small random lateral deflection, and these accumulate.

Robotic putting machines, which eliminate every source of human inconsistency, still only make about 80% of 16-foot putts.17 That missing 20% is the noise floor of the system—the combined effect of dimple error, micro-imperfections in the green surface, and the fundamental geometry of a dimpled sphere rolling on an imperfect surface.

No putter can fix this. No milling pattern, no MOI number, no torque profile. It is a feature of the ball and the green, and it puts an absolute ceiling on what equipment optimization can achieve.

• • •

So What Should You Actually Do?

The physics doesn’t tell you which putter to buy. It tells you which questions to ask about your own game.

What is your primary miss? If you consistently start putts on the wrong line—pushes, pulls, inconsistent starting direction—your problem is face angle control. A lie-angle-balanced design might help by removing one torque variable. A putter matched to your stroke arc (toe hang for an arc, face balanced for straight-back-straight-through) will also reduce timing demands. Face milling won’t help.

What is your contact pattern? If you spray the ball across a wide area of the face, high MOI will tighten your distance dispersion. But if that high-MOI design has a deep CG, you may be trading distance consistency for directional error. Look for designs that achieve high MOI with the shallowest possible CG—weight placed at the heel and toe, close to the face plane.

How repeatable is your stroke? If you have a tight, repeatable arc with consistent tempo, a blade gives you the most honest feedback and the shallowest CG for directional accuracy. If your stroke varies—particularly under pressure, or when you change putt length—a more stable platform (higher MOI, lower torque) reduces the penalty for your worst swings.

What are you actually practicing? No equipment change substitutes for developing the motor control to deliver the face within a degree of square. A putting stroke driven by the shoulders, with minimal wrist action, a consistent rhythm, and a stable pivot produces the most repeatable face angles. Equipment can reduce the penalty for your worst miss, but only practice can shrink the size of the miss itself.

• • •

The half-millisecond of impact doesn’t care about brand names, tour endorsements, or how the putter looks at address. It cares about where the face is pointing, how fast the head is moving, and where on the face the ball makes contact. Everything else—the design, the materials, the balance, the milling—is in service of helping your particular stroke deliver those three variables as consistently as possible.

The best putter for your game is the one that corrects for your weaknesses, matches your stroke mechanics, and stays out of the way of whatever you already do well. The physics is indifferent to aesthetics, tradition, and price point. It rewards the golfer who understands what their stroke actually needs, and who practices the one skill no equipment can provide: delivering the face, within a fraction of a degree, at exactly the right moment.

That’s putting. Everything else is commentary.

Sources & Further Reading

  1. Cochran, A. & Stobbs, J. The Search for the Perfect Swing. Lippincott, 1968. The foundational text on golf impact dynamics, establishing that the clubhead behaves as a free body during the ~0.5ms impact.
  2. Daish, C.B. The Physics of Ball Games. The English Universities Press, 1972. Early rigorous treatment of ball-club collision mechanics and the role of CG position in putting.
  3. Pelz, D.T. Dave Pelz’s Putting Bible. Random House, 2000. Source of the widely cited 83% face angle / 17% path contribution to putt starting direction.
  4. Marquardt, C. The Fundamentals of Putting. Science & Motion GmbH, 2016. Confirms the 83/17 face-path split and analyses face rotation mechanics through the stroke. scienceandmotion.com
  5. Quintic Ball Roll. Face Angle Analysis. Quintic Consultancy Ltd. Independent measurement data suggesting the face angle contribution may be as high as 92% for putters. quinticballroll.com
  6. Wood, P. et al. The Role of Friction and Tangential Compliance on the Resultant Launch Angle of a Golf Ball. Proceedings, 49(1), 27, 2020. Hertzian impact model with Coulomb friction demonstrating how the face-to-path launch ratio varies with club type and friction coefficient (~0.4 for putters). doi
  7. Lambeth, J.M. et al. Exploration of Center of Gravity, Moment of Inertia, and Launch Direction for Putters with Ball Speed Normalizing Face Properties. Proceedings, 49(1), 2, 2020. Key study using adjustable CG/MOI putter showing 0.23° vs. 0.59° offline for shallow vs. deep CG on 15mm toe strikes. doi
  8. Quintic Ball Roll Lab USA. MOI Forgiveness Testing. Independent robotic testing comparing Anser-style blade vs. high-MOI putter on center and ½” off-center impacts. Published by Cure Putters. cureputters.com
  9. Brouillette, M. Putter features that influence the rolling motion of a golf ball. Procedia Engineering, 2(2), 2961–2966, 2010. Demonstrated that face inserts and grooves modulate COR but do not get the ball rolling earlier for fixed-length putts. doi
  10. Penner, A.R. The physics of putting. Canadian Journal of Physics, 80(2), 83–96, 2002. Comprehensive putting physics model establishing that pure roll occurs after ~20% of total putt distance. pdf
  11. Lindsay, N. Topspin in putters — A study of vertical gear-effect and its dependence on shaft coupling. Sports Engineering, 6, 81–93, 2003. Theory and measurement of topspin generation via vertical gear effect as a function of CG height and depth.
  12. Grober, R.D. A Force Model for the Tempo and Timing of Putting. arXiv:0903.1762, 2009. Models the putting stroke as a driven damped oscillator, showing consistent tempo arises from driving the system at resonance. arXiv
  13. Suda, K. et al. An analysis of the putter face control mechanism in golf putting. Sports Engineering, 12, 23–29, 2009. B-matrix analysis showing face rotation is coupled to translational stroke forces through off-diagonal inertia terms. doi
  14. Richardson, A.K., Mitchell, A.C.S. & Hughes, G. The effect of dimple error on the horizontal launch angle and side spin of the golf ball during putting. Journal of Sports Sciences, 2017. Quantified dimple-induced directional error during putting with mechanical arm and human participants.
  15. Cross, R. & Nathan, A.M. Experimental study of the gear effect in ball collisions. American Journal of Physics, 75(7), 2007. Demonstrated that dimpled ball surfaces produce unpredictable rebound angles from flat surfaces.
  16. Cross, R. Physics of Golf. University of Sydney, 2006. Experimental demonstration that golf balls do not roll straight on flat horizontal surfaces due to dimple-surface interactions. usyd.edu.au
  17. Pataky, T.C. & Lamb, P.F. Effects of physical randomness training on virtual and laboratory golf putting performance in novices. Journal of Sports Sciences, 36(12), 1355–1362, 2018. Established that robotic putters sink only ~80% of 5m putts due to irreducible ball-green randomness.