It can be made to be a sine plate. if the round clamping bar is 2 3/4 diameter, the plate is 1" thick, a 3/8 bar mounted six inches from the center of the clamping bar and that (the clamping bar) is located so that the plate is horizontal and the clamping bar can pivot around it's center, it can be used as a sine plate, putting a stack of joe blocks under the 3/8 bar.
I'm not sure this is a good explanation, but if you're sharp enough you can figure it out. I did.