This gets the name Chronos because it mimics a hunting watch—i.e. a pocket watch with a protective dial cover. This one even has a little fob so you could tuck it into a pocket and wear it like a watch (it's diameter is about the same as my big silver railroad watch, but about twice as thick). Another version was available with a wrist watch strap. Considering its size, I doubt many people used it that way.

Anyway, you push a little button and the top of the meter flips up and two little doors in the front fly open so the meter can see. You aim it at your subject and read the light level, and turn the little calculator dial to read your exposure. When you fold the top the little doors pull themselves back in, and it's ready to go back into your pocket. Cute as hell.

There are a couple versions of this, but they're very minor. I have another one that's almost identical except for small difference: the case cover with the Bertram logo has no silver ring around it, the aperture and shutter rings on the inside dial have two ranges with intermediate values, and there's only an ASA speed window: nothing for DIN or Scheiner. And the watch fob is velvet (or something like it) rather than cloth. But ultimately it's the same thing.