This is the Hasselblad E12 6x6 back with ISO control. Hasselblad made three basic types of film magazines, the "A", "E", "E-CC". They are all compatible with all Hasselblad cameras.
The "E" type is designed for Hasselblad 200 Series cameras and is equipped with a dial to program the film speed along with electronic databus connections which work with the camera's metering system by relaying the ASA of the film.
This back will also work on the 500 series, but the electronics will not interface. It will act as a manual back.
It is in good condition with moderate wear. The light seals are good and the back works perfectly.