Sorry for being obtuse. The Synchro Compur used on Rollei and a few other cameras in the 1950 and 1960's had an interlock device on which one could set the EV number and it would lock all aperture-shutter speed combinations from which the photographer could choose. It was intended to be an aid to the photographer. I like it but a lot of folks found it to be annoying.
Originally Posted by afrank