The Ronda 223P-21 watch movement is built on a modified ETA base plate, which is specifically signed as ETA 900. The differences between the CE4 and CE14 are currently unknown. The movement features a manual winding function, a sub second subdial, a day function that can be set by adjusting the time between 20:15 and 24:00 hours, and a date hand that can be quickset by repeated pushing of the crown. The Ronda 223P-21 movement was used during approximately the 1950s.