A pro trick for calculating break is to identify the line that runs straight uphill through the hole, and from the ball, aim at a point on this line about two feet above the
hole. This is a crude version of the Zero Break Line (ZBL) method articulated by H.A. Templeton in his marvelous book,
Vector Putting: The Art and Science of Reading Greens and Computing Break (1984). The ZBL method brings some scientific rigor to green reading, by combining the physics of gravity and a rolling sphere with the speed of the putt, the green's playing speed and the contour of the surface. And in the final analysis, the ZBL method gives you some reliable rules of thumb you can use to improve your reading of
break.
The Science
Most greens average around 3% of slope. For a green oval in shape with the long axis 100 feet in length and aligned with the fairway, rising from front to back, the back edge is three feet higher than the front edge. Greens typically require a minimum of 1% to 2% for effective drainage, so 3% is moderate. Standing at the front edge, the back edge is about level with your hips; if you
squat at the front edge, your eyes are about level with the back edge. If the surface of such a green is tilted but otherwise everywhere flat, with the pin located dead center, 50 feet from either the front of the back edge, the ZBL connects the front and back edges and runs through the hole.
Any putt starting anywhere on this line is a straight putt, uphill or downhill, and all other putts are breaking putts. Any putt starting off this line will break downhill in the direction of the ZBL. The key is to know some basic rules of thumb for telling how much a ball will break toward the ZBL.
The actual "break" of any putt can be known from the position of the ball on the green (in relation to the hole and ZBL), the putt speed, the green speed, and the slope. This allows the golfer to spot the aim point for the putt, as a point along the ZBL above the hole. For purposes of simplification, all putt speeds are such that the ball would stop about one foot past the hole if it missed. This isolates green speed and slope.
The green speed and tilt / slope determine how far above the hole on the ZBL the aim point will be, regardless of where the ball is located on the green. Green speed is here understood to mean Stimpmeter reading. This is the distance a ball rolls across a level part of the green after being launched by rolling it down a 30" inclined plane with the back of the plane raised one foot above the surface. A "Medium Fast" green is one on which a Stimpmeter rolls a ball 7'6".
An Example
Assume the oval green is 100 feet long and 80 feet wide, with the pin in the center, and the ball pin high 10 feet away. The green is flat but tilted 3% from front to back on the minor (80') axis. If the aim point is somewhere on the ZBL above the hole, how high up is it? What do you need to know? Green speed and tilt.
Green speed. The "faster" the green speed, the slower the putt for the same distance and the greater the break. Hence, the faster the speed, the higher up the ZBL the aim point is located.
If you putt straight at the hole, the ball will break downhill. For a 3% slope on a Medium Fast green, the force of gravity will make a ball change its direction of roll about 17 degrees. Over the 10' putt, this change of rolling direction downhill makes the ball "break" about 10" below the hole. So your aim point in this case is 10" ABOVE the hole on the ZBL.
If you marked this spot with a golf tee, it very nearly would be your aim spot from ANY and ALL ball locations on this green. On uphill breaking putts, where the ball has to roll faster, thus with less break, the aim spot is a touch lower on the ZBL. For downhill breaking putts, where the ball has to roll slower, thus with more break, the aim spot is a touch higher on the ZBL.
Whenever the ball is below pin high, the actual "break" will increase from the straight-uphill putt to the putt from pin high, and then as the ball position rises higher above pin high the "break" will diminish until the straight-downhill putt. But in every case, the aim spot will stay the same for the same length putt.
Hey! That's an EASY rule of thumb -- when the green slope is average (about 3%) and the speed is a bit fast (about 7'6"), the aim spot is on the ZBL above the hole about one inch for every one foot of putt. Neat rule!
Thus, for a 20-foot putt, the aim spot is about 20" up the ZBL. For a five-foot putt, the aim spot is about 5" above the hole.
Also, this 10" also works for straight uphill or downhill putts: aim 10" past the hole for uphill putts and 10" short of the hole for downhill putts where the green tilts 3% and runs 7'6" medium fast.
Other Green Speeds. Using the following range of Stimpmeter speeds, the aim spot varies about one inch lower for each one-foot drop in Stimpmeter speed. Another neat rule!
All for 3% slope:
Slow (Stimpmeter 4'6") aim spot 6" above hole on ZBL.
Medium Slow (Stimpmeter 5'6") aim spot 7" above hole on ZBL.
Medium (Stimpmeter 6'6") aim spot 9" above hole on ZBL.
Medium Fast (Stimpmeter 7'6") aim spot 10" above hole on ZBL.
Fast (Stimpmeter 8'6") aim spot 11" above hole on ZBL.
Other Slopes. The general rule is that the aim spot climbs or descends along the ZBL in the same proportion that the other slope is to 3%. In other words, if the aim spot is 10" on a 3% slope, the aim spot on a 1% slope will be one-third as high (10" x 1%/3%), or about 3" up the ZBL. For a 5% slope, a 10" aim spot on a 3% slope becomes about 17" (10" x 5%/3%). Actually, as the slope increases, the aim spot goes a little higher than this, so add in a "tip" of extra height (about 20% or one-fifth of whatever you come up with in extra height for the aim spot). So a 5% slope really has an aim spot about 20" high. A 6% slope, twice that of a 3% slope plus a "tip," changes a 10" aim spot to a 20" plus 4" or 24" aim spot.
The rule of thumb, then, is: For less than average slopes, reduce the height of the 3% aim spot by the proportion of the lesser slope to the average slope. For slopes steeper than average, increase the height of the aim spot by the proportion of the greater slope to the average slope plus a "tip."
Make This Part of Your Game
Obviously, not many greens are flat albeit tilted. Still, with top dressing, mowing, weathering, drainage design features, and dictates of fairness in hole placement, putts quite often run over pretty uniformly sloped sections of the green. The ZBL technique lets you get a pretty good handle on the situation.
There is really only one rule and two modifications away from the average slope and green speed. To simplify, when your putt runs mostly over level but tilted ground, find the line of zero break through the hole, or the line that runs straight uphill through the hole. Then, assess green speed and slope.
For a medium fast green, pick an aim spot on this zero break one inch up for each foot of your putt. If the slope along the ZBL appears to be about 3% or pretty average, you're in the ballpark with this aim spot no matter where your ball is
located. If the green looks pretty level, closer to 1%, reduce the aim spot to one-third. If the green looks fairly steep, closer to 6%, double the height of the aim spot plus a 20% "tip."
If the speed of the green is not medium fast, add or subtract about one inch for each foot of Stimpmeter reading above or below the medium Fast speed.
Don't have a Stimpmeter? That's okay; just make a core putt. If the putt rolls about the same length as a standard flag pole (7') or a bit more, you're probably on a Medium Fast green, so use the "one inch per one foot of putt" rule to get in the ballpark. In every case, putt the ball with a speed that goes about one foot past the hole if you miss. Not TOO complicated, eh?
