hi trask
if your rolleicord is like the one i had ( i had a 1 a /3 )
the ruby window is primarily for only finding frame #1
and the camera has a mechanism to wind to the next frame
so you don't have to keep looking at the ruby window.
there is a little button you pressed when you lined up #1
and at the same time you pushed a the button in the center of the
wind-knob and it resets the internal frame counter mechanism ...
some old folding cameras have a similar
here's a little utub vid that shows how to use it