These two are extinction meters, sometimes also called optical meters. There are no electrical components: no cell, no ammeter, no wires. It was pre-photo-electric technology that continued to sell because it was 1/8th the price of even a mediocre selenium meter. It's fun to read some of the ads because they try to play up all the virtues: won't break if it's dropped, can be used in the rain, it's small and light and a very inexpensive.

Extinction meters worked on the idea similar to a step wedge, where each section was progressively more dense and harder to read the number or letter in it.

So you peep through this thing and see which is the last letter than can be reasonably seen, because the more light, the more letters will light up; the less light, the fewer.

The outside cylinder of this thing is the exposure computer. The top of the cylinder turns, so you match up the letter to an arrow, then find which column matches your film speed, and that gives you your speed/aperture pairs.

A nice touch: the eyepiece can be adjusted to focus on the strip inside, so you can use it without glasses.

I have two. One is the original DREM made in Austria. DREM is an acronym for "Dr. Emil Mayer," and they made a lot of variations of this meter with slightly different names. It's marked only in Scheiner. I also have one that was made in the USA that is the same thing, except that it's marked in both Scheiner and Weston numbers.