The Ronda 313P-21 watch movement, also known as the 158 movement, is a manually-wound mechanical movement that was predominantly used around the year 1965. It features a pin-lever escapement and includes a sweep seconds function. The movement incorporates an indirect minute hand friction clutch on the barrel and utilizes a stem mechanism without a setting-lever spring. The Ronda 313P-21 movement is typically identified by its signature marking as 158.