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Putting greens are the most important playing surface on a golf course and their condition and playing quality are understandably the focus of considerable attention from golfers and superintendents. In the 1970s, the USGA released the Stimpmeter to help golf courses objectively measure putting green speed. This tool was designed to help superintendents maintain appropriate and consistent green speeds across their course. However, green speed alone provides an incomplete picture of putting green quality and faster has often been misconstrued as meaning better. In an effort to broaden our understanding of putting green playing characteristics, the USGA developed a tool in the 2000s to measure putting green firmness. This tool has been used by our agronomists at USGA championships for almost two decades, and similar devices are used at golf courses around the world.

To help superintendents measure and communicate a more complete picture of putting green quality, the USGA designed the GS3 ball to objectively measure putting green speed, firmness, smoothness and trueness in a single device. The GS3 provides green speed measurements based on the rate of deceleration of the device. This data is translated into a green speed number in feet and inches that is comparable to a traditional Stimpmeter reading. We will not spend time in this article exploring green speed ranges because this metric is very familiar to most superintendents. However, most golf courses have never measured firmness, smoothness or trueness in an objective way. Now that the GS3 has been in use for more than a year at golf courses across the budget spectrum and at USGA championships – including the U.S. Open – we have learned a lot more about what different readings for these metrics mean.
 

The ranges provided below are meant to help GS3 users understand the measurements they collect. Every course should spend time developing their own benchmarks for each metric because there can be considerable variability in what constitutes desirable and undesirable readings based on turfgrass species, local weather, putting green age, soil characteristics and golfer expectations. We encourage courses to view these metrics in the context of a target range rather than a specific number, and to recognize that your target ranges will likely change throughout the year. To get the most benefits from data collection, it should be a consistent process over time. There may be opportunities to improve and learn more no matter how well your greens are performing.

The reference ranges in the sections below are all based on collecting data shortly after morning maintenance ends, but before play begins. Values for these metrics have the potential to change throughout the day depending on precipitation, grass growth, foot traffic and cultural practices. These ranges apply to all grass types, though the averages within these ranges can be expected to vary based on turf type.

Firmness: You measure firmness with the GS3 by placing the device in a special drop fixture that allows you to drop it from a consistent height. Sensors inside the tool measure how far the drop fixture penetrates into the putting green surface in inches to provide the measurement, with lower numbers indicating firmer conditions. Multiple firmness readings should be taken across each green to develop a complete picture because individual measurements can vary significantly by location – even within the same green.

Typical Range of Values: 0.300” – 0.500”

  • 0.300” – 0.350” Extremely Firm
  • 0.350” – 0.400” Firm
  • 0.400” – 0.500” Likely suitable for most facilities
  • >0.500” Receptive
     

Smoothness: The GS3 takes smoothness measurements during a normal roll from the Stimpmeter. This metric refers to the magnitude and quantity of vertical deviations while the GS3 rolls across a putting green surface. Put simply, it measures vertical bouncing and higher numbers indicate less smoothness. The following ranges describe how to interpret the average smoothness result of three rolls in opposite directions, for a total of six rolls. This is the recommended procedure for performing a roll test with the GS3 for speed, smoothness and trueness – all of which are collected simultaneously by the tool.

Typical Range of Values: 0.0 – 16.0

  • 0.0 – 5.0: High-quality ball roll with minimal vertical deviations.
  • 5.0 – 8.0: These values fall outside the normal range.
  • >8.0: Averages consistently above 8 are typically only seen after disruptive cultural practices and should improve with growth and recovery.

 

Trueness: The GS3 takes trueness measurements during a normal roll from the Stimpmeter. This metric refers to the magnitude and quantity of horizontal deviations during the roll. Golfers would call this type of deviation “wiggle” or something similar. Higher numbers indicate a less-true ball roll. The following ranges describe how to interpret the average trueness result of three rolls in opposite directions, for a total of six rolls.

Typical Range of Values: 0.0 – 7.0

  • 0.0 – 1.0: High-quality ball roll with minimal horizontal deviations.
  • 1.0 – 1.5: These values fall outside the normal range.
  • >1.5: Averages consistently above 1.5 are typically only seen after disruptive cultural practices and should improve with growth and recovery.
     

What have we learned?

USGA staff have worked intensively with researchers and superintendents to better understand how to use the GS3 and what the numbers mean in terms of real-world playing conditions. We have learned many lessons from that work, including the following:

  1. Collecting objective data about a range of putting green characteristics is a great way to guide management programs and communicate with stakeholders. When golfers and decision-makers can see how speed, firmness, smoothness and trueness vary throughout the year, and from year to year, they develop a better understanding of how the course is performing against expectations and the impact various maintenance practices have on playing conditions.

  2. The most difficult hurdle to overcome in using the GS3 to guide management programs is consistent data collection. The more consistent your data collection program is, the more useful the data will be for making decisions. You don’t need to take measurements on every green every day, but you want to establish a consistent data collection program as part of your maintenance routine. Find a system that works for you and your facility. The Green Section Record article “A Quick-Start Guide to Putting Green Data Collection” offers some helpful strategies.

  3. Collect GS3 data for multiple months before establishing target ranges for your putting greens. Seasonality, weather, maintenance budget, architecture and golfer ability are all factors to consider.

  4. During USGA championships or professional tournament golf, the golf course is being optimized for a very short time with resources that are simply not available for routine maintenance. Surface performance values for championship play are typically inappropriate for daily play. For daily play, golf courses need to balance surface performance with available resources and turfgrass health.

  5. Your performance metrics only apply to your golf course. These values should be used to track putting green performance over time at your course, not to compare your course to others. There are far too many variables involved for fair comparison of these metrics among golf courses.

  6. Incorporate multiple metrics beyond GS3 measurements to evaluate progress including golfer feedback, organic matter content, and clipping volume. Record your inputs and understand what was required to deliver the measured playing qualities. Evaluate your program critically to see if there are ways to reduce inputs and still maintain your desired surface performance.

  7. Focus on consistency. Do not push for dramatic alterations in surface performance for short periods of time. Consistency is key to providing a quality golf experience while maintaining sustainable, healthy turfgrass.

     

We have more to learn

The USGA is very proud of the GS3 but there is still much to learn with a tool that is relatively new. We have partnered with multiple universities to continue evaluating putting green performance with the GS3 and to see how the tool performs over time, under rigorous scientific testing. Our internal research and university partnerships have produced many improvements in the two years we have been using the tool, including an overhaul of our firmness algorithm that now delivers more-reliable results. The more we learn about data collection and putting green management, the more questions we have and the more opportunities our industry has to improve. Please don’t hesitate to reach out with questions. We can be reached at greensection@usga.org.