The Stimpmeter is a device used to measure the speed of a golf course putting greenby applying a known force to a golf ball and measuring the distance traveled in feet.
The device is an extruded aluminum bar, 36 in long and 1.75 in wide, with a V-shaped groove extending along its entire length, supporting the ball at two points, half an inch apart. It is tapered at one end by removing metal from its underside to reduce the bounce of the ball as it rolls onto the green. It has a notch at a right angle to the length of the bar 30 in from the lower tapered end where the ball is placed. The notch may be a hole completely through the bar or just a depression in it. The ball is pulled out of the notch by gravity when the device is slowly raised to an angle of about 20°, rolling onto the green at a repeatable velocity of 6.00 ft/s. The distance traveled by the ball in feet is the 'speed' of the putting green. Six distances, three in each of two opposite directions, should be averaged on a flat section of the putting green.
One problem with most modern greens is finding a near level surface as required in the USGA handbook. Many greens cannot be correctly measured as you cannot find an area where the measured distance or green speed in opposing directions is less than a foot, particularly when they are very fast requiring a very long level surface.
The USGA stimpmetered putting greens across the country to produce the following recommendations:
Slow greens: 4.5 feet
Medium greens: 6.5 feet
Fast greens: 8.5 feet
For the U.S. Open, they recommend:
Slow greens: 6.5 feet
Medium greens: 8.5 feet
Fast greens: 10.5 feet
Some of the fastest greens in the world are at Oakmont where greens speeds can reach 13-15 feet