example of 2 faces
the one picture is deceiving as it shows both faces at the same time, it's just combining the 2 so you can see both side by side.
the original reverso is from 1931 and is only just over 2mm thick, has a clean back on it, and just a simple face. the idea behind it was the first sports watch. when you didn't want to take it off to play sports, you just flipped the face around to protect it.