Model: Horvex 3
Cell type: Selenium
Measure type: Reflecting/Averaging
Metrawatt of Germany made the Horvex line of meters, of which there are three major versions. The original came out just before the war. The Horvex 2 is from the mid-50s, and this 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.
There only apparent difference between this and the Horvex 2 appears to be the arrangement of the calculator dial; the older model has Weston, ASA and DIN; this one drops Weston and adds an EV number window. Also, the back (mouse over to see it) has a diagram that explains how to use the meter.