Automatic mechanical watches. The idea that this tiny device is assembled entirely from macroscopic, tangible, "grokkable", mechanical components, will run "fo

Automatic mechanical watches. The idea that this tiny device is assembled entirely from macroscopic, tangible, "grokkable", mechanical components, will run "forever" with no direct conscious input of energy and tells you reasonably accurate time is pretty unique. Recent relevant HN thread https://news.ycombinator.com/item?id=13459616 https://news.ycombinator.com/item?id=13459616