The Rank Mamiya is a rangefinder camera from an era when camera manufacturers were establishing themselves in certain markets. Mamiya has a long and great history in medium format cameras but never really established themselves as a force in the 35mm market.
This camera is a bit of chameleon as it goes by a number of names, including Rank Aldis, Mamiya Ruby and Mamiya 4B. Also related is the Mamiya M3, which would never be confused with the namesake in the Leica world. Some of these models have a few differences but are essentially the same camera.
The Rank Mamiya is a 35mm rangefinder camera with a fixed Mamiya-Sekor 40mm f/2.8 lens. It uses an uncoupled selenium meter, so it does not take batteries. It is housed in a chrome body with black fake leatherette covering for grip and wear.
The top plate has an Exposure Value (EV) indicator, where the selenium meter will suggest the exposure settings in EV numbers. These are then used when adjusting exposure on the lens, by adjusting the combination of aperture and shutter speed to show the indicated EV number.
Also on the top is the shutter release, with standard remote thread, and the frame counter which is around the film advance lever. The frame counter has to be reset manually each time you load film. A cold shoe and the rewind crank are also on the top.