The A. Schild 1583N watch movement, similar to the ETA 2520, incorporates Kif shock protection. It features a different rotor shape and an anodized alumina barrel with lifetime lubrication. Although the differences between the 73 and 623 are unknown, it is believed that the designators were changed in 1966, as samples with both numbers have been observed from this year. The A. Schild 1583N movement is an automatic movement with sweep seconds and was used around the period of 1966.