Measuring Green Speed with iOS Devices

February 21, 2012

 Marcus Jones, PhD, Iowa State University and
 Quincy Law, Graduate Student, Purdue University 


The iStimp App
By now, you have probably heard of the iStimp, an app developed by, to measure green speed. The iStimp is available to anyone who has an iOS device such as an iPod Touch, iPhone, or iPad for a nominal fee of $0.99. A stimpmeter reading is obtained by rolling a golf ball off the iOS device and measuring the distance the ball travels with a built in ruler. The iStimp application then uses algorithms to generate a stimpmeter value.

With over 250 million iOS devices sold to the public, the iStimp may have already appeared at your facility. If not, chances are you will at some point in the future. The question is, does the iStimp produce stimpmeter readings equivalent to what you generate with the USGA stimpmeter? A study conducted at Iowa State University set out to answer that question.

How we did it
Our study was conducted on a practice putting green at a local area golf course. The turf was a mixture of creeping bentgrass and annual bluegrass mowed at 0.125 inches.  Wind speed was negligible during the test.

Stimpmeter readings were obtained using the iStimp app with an iPad 2, iPhone 4, and iPod touch 4th generation. The USGA stimpmeter was included as a control along with a research stimpmeter which is known to produce equivalent stimpmeter readings.

Three people, each with varying experience using stimpmeters, operated each device. All accessories (cases, ect.) were removed from each iOS device with the exception of screen protectors.

A level area of the green was selected and a tee was inserted at the end of the measurement device. Three golf balls were released, one at a time, from each device according to the guidelines suggested by the manufacturer. Titleist Pro VI golf balls, each weighing within one gram of the others, were used in this study.

The distance each golf ball traveled was measured from the end of each device to the front of the golf ball. The built in ruler function was used with the iOS devices and a measuring tape was used to record ball roll for the USGA and research stimpmeters. This length was recorded for each golf ball and the average obtained. The same three golf balls were rolled in the opposite direction along a similar line and the same measurements and calculations performed.

Accuracy of the iStimp
The green speed of the putting surface was 12 feet according to the USGA stimpmeter (Figure 1). This device is the only tool accepted by the USGA to measure green speed. The research stimpmeter produced a statistically similar reading of 11.8 feet. Research stimpmeters have proven to yield green speed values similar to the USGA device. The fact that the USGA and research stimpmeters produced statistically similar values in our experiment verifies our technique.

The three iOS devices equipped with the iStimp app failed to produce stimpmeter values similar to the USGA device (Figure 1). The iStimp application when utilized on the iPad 2 underestimated stimpmeter readings by 9%. In contrast, the iStimp application overestimated stimpmeter readings on the iPhone 4, and iPod touch 4th Gen. by 21 and 16%, respectively.

Figure 1. Stimpmeter readings for five devices used to measure putting green speed.  Columns with different letter are statistically different.  Note: Stimpmeter readings are listed in feet: 14.5 = 14’6”.

If golfers approach you and want to discuss stimpmeter readings obtained from the iStimp, take the time to find out which device they used. While the iPad 2 generated readings most similar to the USGA stimpmeter, this seems the least convenient device to obtain stimpmeter readings with due to its size and expense. There are probably far more iPod’s and iPhone’s that find their way onto golf courses and each of these devices will overestimate stimpmeter readings.

Regardless of the iOS device used, stimpmeter readings obtained with the iStimp app on the iPad 2, iPod touch 4th Gen. and iPhone 4 are different compared to the USGA stimpmeter and comparisons are not valid.