The E magazines are for the 203FE and 205FCC cameras and automatically connect to the camera's exposure metering system. The film speed is programmed on the magazine. On the back of the magazines there is a slot for the magazine slide when it is not in use.
The E12, E16 and E24 magazines have the same features and mechanical functions as the A12, A16 and A24 magazines. The film speed programming dial and the differences in the exterior design are shown below.
Film speed programming dial
Magazine slide holder