Mine's like "ER" or something like that so if that's correct it would be May 1979. It's in the My Photocells album in my gallery somewhere. Is yours thermal too?
It has a time delay sticker on the cover. I opened it up once and it looks different inside. If it is thermal, it's unlike any thermal photocontrol I've seen before.
Mine's got a delay like a thermal but I forget what the insides look like. Dunno if I've ever even opened it. It has an adjusting feature that tilts the CdS eye so that only part of it is exposed to the window to alter the sensitivity of the unit.
Yeah I noticed that feature too. If you loosen the two screws near the base, you can rotate the cover so part of the eye is not exposed. I also noticed the window on mine is really thin.