The Eterna 1020S watch movement is a hunter calibre with options including a bimetallic screw balance and a Breguet hairspring. It is available in different heights, namely 4.1mm, 4.75mm, and 5.0mm, and features various bridge shapes depending on the version. These calibres, although poorly documented in literature, have different variations recorded under the designation 99. In this archive, the calibre number 99 is extended by construction height and generation number. The Eterna 1020S movement is capable of stem winding and setting, has a sub-second function, and was used around the period of approximately 1928.