The Eterna 1423U watch movement is an automatic movement with a sweep second function. It shares similarities with the ETA 2520 movement, but it incorporates Kif shock protection and features a different rotor shape. Additionally, it possesses an anodized alumina barrel that ensures lifetime lubrication. Although the exact differences between the Eterna 1423U and 623 movements are not known, it is speculated that the designators were simply changed in 1966. Samples of watches with both movement numbers have been observed from that year. The Eterna 1423U movement was utilized around the period of 1966.