RPM is the acronym used for revolutions per minute. It measures the number of revolutions completed in one minute around a fixed axis, giving the speed of a mechanical component. It is commonly used to describe the performance of automobile engines.
Like most ballparks built from the 1990s onward, Safeco Field is a 'retro-modern' style ballpark that incorporates many of the features of ballparks built in the 1950s and earlier with modern amenities.
In professional parks, the field is surrounded by an area roughly 10 feet (3.0 m) wide made of dirt or rubberized track surface called a warning track. Originally used in Yankee Stadium in 1923 as an actual footrace track, it is now present in all major league ballparks.