A stimpmeter is used to measure how quick the speed of the green is
The speed of greens is a talking point from Tour events to weekend medals. Speeds are measured with a device known as a Stimpmeter, an aluminium bar which is raised to an angle of about 20 degrees so a ball can run down its length and along a at part of a green. The distance the ball rolls is measured in feet, which is then the speed of the green.
The fastest greens in the world – like those at Augusta National for the Masters – run at about 12-15ft on the stimp (we'll never know for sure because the club doesn't talk about it), whereas the greens at a normal UK club would be about 6-8ft. This table below shows different green speeds produced by the USGA: