In a box of assorted old stuff, I found something that is obviously a secondary lens for a twin lens reflex. The plastic case it is in says PLUS-PARALESS-UP - GRC. The upper lens says Plus Brand Paraless-Up. The bottom lens says O.K.C. Pat. Pen. 30cm - 50cm. It's obviously Japanese because the cardboard box it is in has only Japanese on it.
AH -HA I JUST DISCOVERED WHAT IT DOES. When you turn the upper lens it move its image up a down. It's a paralax adjustment. I guess the 30cm - 50cm is the distance from the camera it will adjust for. I'll have to see if it will fit on my Yashica.