Model: Movie Meter
Price (new): $8.95
Cell type: Selenium
Measure type: averaging
Sankyo was one of the Japanese electronics companies which took over the US market in the 1960s, and movie cameras were part of the flood.
This little meter is shoe-mount so you can use it on anything with an accessory shoe, but it's obviously meant to clip into one of their cine cameras. Which one, I don't know. It's battleship gray and about the size of a thick cigar butt. If you mount it onto a horizontal shoe, the meter scale is on the top and easy to read.
There's not much to it: it's direct reading for (I assume) 16 fps and around 1/30th second, so you turn a collar to set the film speed in ASA, and then direct-read the aperture.