The Derby 40 watch movement was produced from 1912 to 1966, with a total of 4,903 units. There were two distinct periods of production. The first period, from 1912 to 1963, saw the production of watches numbered between 16,000 and 16,680, with 167 of them being certified by observatories. The second period, from 1932 to 1966, produced watches numbered between 200,826 and 205,047, 131 of which were certified by observatories. Unfortunately, the exact fraction of movements with the split-second function is unknown. The Derby 40 movement is a stem-wind chronograph rattrapante with a 60-second counter and a 30/60-minute counter. It features pillar wheels for smooth operation and includes a sub-second display.