The Laco 550 is an open face calibre watch movement featuring a stop function with a pillar wheel. It is likely manufactured by AS, but can also be found listed as Heuer 943, Heuer 960-987, and Leonidas 943. These listings are mostly similar with occasional minor differences, and sometimes have incorrect diameters of 19'''. The movement includes various functions such as a timer (with options for 60s or 30s intervals), stem wind, sweep second, and timer and split-second functions. The Laco 550 was commonly utilized around the period of 1925.