The Swatch Sistem51, introduced in 2013, is an automatic watch with a movement made of only 51 parts, assembled by a fully automated process and held together by a single central screw. It has a plastic or Irony-steel case, a power reserve of about 90 hours and a transparent dial or back through which the movement can be seen, and the whole watch was priced at under 200 US dollars at launch. I did not find reliable official figures for the case size of the first models.

The movement was developed by Swatch Group engineers to be produced cheaply and in large numbers, and its small number of parts is a reference to the Swatch’s original 51-part plastic watch. The calibre is sealed after assembly and is not designed to be opened.

The community praised the Sistem51 as proof that a mechanical watch could be both cheap and well made, though some noted it cannot be serviced in the traditional way. Swatch still makes Sistem51 models, so the line remains in production.