In India, locomotives are classified according to their gauge, motive power, the work they are suited for and their power or model number. The class name, composed of four or five letters, encodes this information. The first letter denotes the track gauge; the second denotes their motive power, diesel or alternating current (electric); the third letter denotes the type of traffic for which they are suited (goods, passenger, multi or shunting). The fourth letter used to denote the chronological model number, but from 2002 it denotes the horsepower range for diesel locomotives. Electric locomotives are not covered by this scheme and not all diesels are covered; for these, the fourth letter denotes their chronological model number.