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.