A mechanical watch has gears that are turned by a spiral spring – called a mainspring. Energy is stored in the mainspring by turning the crown on the side of the watch. The energy from the mainspring powers the watch movement until it runs down, requiring the spring to be wound again. An Automatic watch, also known as a self-winding watch or simply an automatic, is a mechanical watch that has an additional mechanism which winds the mainspring using the natural motions of the wearer’s body.