The 218s are much more conventional: they have a stem and crown although this is usually at the 4 oclock position; they can take a modern 1.5 volt Silver Oxide battery without any adjustment; and there are no 218 Spaceviews that reached market.

Some 218s had a second crown at the 2 oclock position. Depending on the model, this second crown did different things. In the first picture below, it allows the setting of the second time zone hour dial on this Astronaut Mark II. In the second picture, we have a Deep Sea 666 Feet and the second crown allows rotation of the inner bezel.

Is the Accutron in the third picture the rarest of all Accutrons? Must be a contender for that title. Certainly the case is the most unsual of all Accutrons (and many other watches for that matter!).

There are various versions of the 218 calibre: 218, 2180, 2185, etc depending on whether they had day, day/date or second crown.