Measuring Green Speed on Sloped Putting Greens
Clark Throssell was a first-year grad student at Penn State
University, and I was an experienced fourth-year student.
Stimping is easier with two people, and Clark needed someone to
read measurements while he held the end of the stimpmeter. The
story goes that Dr. Joe Duich, our mutual advisor, sent Clark and
me on a week-long trip to Pittsburgh to assess differences in
green speed among Pittsburgh's many fine golf courses as part
of Clark's thesis project. With virtually no advanced
planning and no roadmap, we trotted off in a rental car in search
of some of Pennsylvania's most exclusive courses.
Getting permission to set foot on these courses was not always
easy. Some superintendents were surprised to see two tired,
tee-shirted students who wanted to check the speed of their
greens. Others were afraid we'd publicize how slow their
greens were. "You should have been here last week before the
rains hit," they'd say.
But those problems paled in comparison to the one we encountered
when we took our measurements. The U.S. Golf Association Green
Section booklet on the stimpmeter explains that readings must be
taken on a reasonably level area. To our dismay, we had one heck
of a time trying to locate representative level areas on which to
take our green speed readings. Whole greens had to be bypassed
because they just weren't flat. This problem seemed to be
worse at the finer courses, the ones with challenging green
architecture and lightning fast speeds. Staying within the
six-inch deviation between forward and reverse readings
recommended in the USGA booklet was nearly impossible.
Furthermore, we were skipping large portions of the golf course
because of sloped greens.
Necessity is the mother of invention. The problem of sloped
greens bugged me for several years after our Pittsburgh study.
One day, though, I sat down and figured out a mathematical
solution to the problem. The solution came too late for Clark,
though. He'd since graduated with his degree in Stimpmeter
Science and was off to Kansas for his Ph.D. I also graduated
shortly thereafter and was off to a faculty position at Oklahoma
State. It was there at Oklahoma State that I was able to do the
field validation work on the devised formula. Ron Hostick, one of
my undergraduate students, was drafted to hold the stimpmeter
while I took readings.
Deriving a formula for correcting green speed readings on a slope
was not as complicated as it sounds. I had some help from Sir
Isaac Newton. After Newton recovered from his apple-induced head
injuries, he penned some of the basic theories of motion physics.
These basic theories were the foundation of my formula for
correcting green speed readings for slope. Who knows? If a stray
hook shot instead of an apple had beaned him, Newton might have
claimed the fame for this new formula instead of me!
Newton described the motion of apples (or any other object)
moving down a slope in mathematical terms. By merging his
equations for up- and down-slope movement into one equation, the
following formula was born:
is the stimpmeter reading taken in the uphill direction, and
is the reading taken downhill.
As simple as the formula looks, it actually works to remove the
effect of slope from green speed readings. In fact, when using a
calculator for the math, computing green speed is no more
complicated than with the traditional two-direction averaging
method the USGA presently recommends. Here's how to use the
- Locate a spot on the green with a uniform surface. The
surface can be on a slope or on a flat area; the formula works
in either case. Try to avoid areas with concave or convex
surfaces, just as you would when reading traditional stimpmeter
speed. Also, avoid shooting crossways on a slope, as the ball
will curl downhill (Figure 3).
- Roll three balls in the downhill direction. Average the
three rolls. Then, roll three in the uphill direction,
averaging these. Plug the downhill average into Sz in the
formula and the uphill average into Sz. The formula will
provide a green speed reading as if the sloped green were
tilted into an upright, level position.
Mathematical theories are of no use unless they're validated
with actual data. Checking the formula on golf course putting
greens was only part of the validation. One problem arises when
testing green speed on putting greens: Stimpmeter speeds can
change from location to location on a golf course, confounding
the ability to validate the formula. For example, comparing a
rough-surfaced slope with a smooth-surfaced level area would be
like comparing apples and oranges.
It was necessary, therefore, to construct a test runway in the
laboratory that could be tilted at various angles and still have
the same uniform surface. This was accomplished by building a
solid wooden runway, 24 feet long, covered with patio grass
carpet. Those of you who've putted on this stuff know that it
stimps about 8 or 9 feet, similar to many putting greens. We
tilted the runway at six different angles from 0 to 5.6% slope
and tested the stimpmeter speed as we changed slope (Figure 2).
Up-slope readings slowly declined with increasing slope, while
down-slope readings began to really take off at slopes above 1 or
As a result, the traditional averaging method of computing
stimpmeter speed began to incur error as slope increased. Using
the formula, however, corrected speeds were equal, regardless of
In our tests on actual golf courses, the formula provided the
same correction factor as in the laboratory. We tested it on
slopes up to 6% and still it yielded accurate results.
"Eyeballing" the amount of slope - or lack of it - on a
golf course is a tricky task, even for professional golfers.
After all, golf course architects design greens with an optical
illusion that makes slope difficult to judge. I took several
students out to a green where I'd placed pairs of flags on
various slopes. Most were unable to distinguish a 2.2% slope from
level. Thus, don't rely on your sight to tell you if
you're on a level area. You'll know you're on a level
surface when the forward and reverse stimpmeter readings differ
by no more than six inches. If not, use the formula instead.
If you're fortunate to have level greens, stick with the
traditional averaging method of calculating green speed - the
formula will give you no better results than the method
you're presently using. But if you have sloping greens, or
sloping spots you'd love to check for green speed, try the
formula. You'll probably agree that the traditional
forward-reverse averaging method is still handier. But for those
sloped areas, the formula will give you accurate green speed
readings that were previously impossible to obtain.
I first became impressed with some of the problems of measuring
green speed 10 years ago when participating in a Master's
thesis project with Clark Throssell, who is presently Associate
Professor, Department of Agronomy, Purdue University. (Well, I
suppose participating is not the best word for my involvement in
his project ~ try drafted.) We found that one of the main
problems in measuring green speed, as I'll explain, was
slope. But first, let me describe how Clark's study got me
involved in green speed research.