This Green Speed Meter (commonly called a Stimpmeter) is a  precision tool used to measure the speed of a golf course putting green. It is an industry standard tool that allows the greenkeeeper to make statistically accurate measurements of the putting surface speed.  

Measurements are taken on a relatively flat part of the golf putting green. A golf ball is placed on the stimpmeter which is then tilted up to the angle at which the ball rolls down the meter and on to the green. The distance travelled by the ball is measured in feet and the process is then repeated multiple times (in opposite directions) to obtain an average distance. This average distance is referred to the Green Speed or Pace.  

examples below:
Slow                     4.5 feet (1.4 m)
Medium                6.5 feet (2.0 m)
Fast                      8.5 feet (2.6 m)

Comes complete with instructions and data sheet.