Metrawatt of Germany made the Horvex line of meters, of which there are three major versions. The original came out just before the war. This Horvex 2 is from the mid-50s, and the Horvex 3 showed up around 1960.

A simple little meter. Aim the little arrow on the calculator dial at the needle and read the pairs. There's another arrow if the accessory photocell is plugged in. That was a Horvex special feature, and common to all their meters.

The only apparent difference between this and the later Horvex 3 is the calculator dial; this model has Weston speeds, along with DIN and ASA. The Horvex 3 dropped Weston and substituted EV numbers instead.

Argus branded them as their L3 model. Exact same meter except for the branding on the dial and the color of the case (the Argus is black).

How to use it: on the outer dial, at the bottom, there's a small piece that has two arrows and the plug-in-accessory icon. On each there's a bent tab. Use these tabs to push and rotate it. That lets you set the film speed in the windows on the inner dial. The left window is for the Weston scale, the right window is for the ASA scale, and the bottom window is for DIN.

Once you have your film speed set, aim the meter at your subject and look for the needle in the bottom window. Rotate the outer ring until the big arrow is pointing to the needle. You want to make sure you follow the path to the needle, don't just point directly to it; you see those alternating black and bare-metal strips? Those are the paths. It's important to do this because the calculator dial scale is longer than the meter face so you can't just match the pointers.

Once you do that, you can read the speed/aperture combinations at the top.

Alexander Belevich was kind enough to provide a high-resolution photo of this meter. Thanks!