Rolleicord V

The red-colored circle in the picture shows the light values.
Usage of light value system.
Set the light value comparing with the scale at the camera back, then set either one of the shutter speed or the aperture.
Once setting the either one, the other one is to set automatically.
The aperture value is indicated at the base of the taking lens beside the light values, and the shutter speed is at the other side.
In addition, Rolleiflex 3.5 was the first that had the light value system built in the shutter unit.