An escalator is a set of electrically-powered moving stairs, driven by chain and sprocket and held in the correct plane by two tracks. It is usually inclined at 30° and limited to a total rise of up to 18 m (60 ft). As the steps approach the landing, they pass through a protective comb-like device. Escalators are used to carry pedestrians between floors in busy areas such as large stored, office buildings, and underground railway stations. The Otis Elevator Company exhibited the first escalator in 1900 at the Paris Exposition.