Barry Abrams

I'm moving a 2 point line using keyframes. I'd like to take those 2 points along with the same 2 points from the previous frame and create a 4 sided primitive. I think it makes sense to do this inside a solver, but I can't seem to get the previous position out of Prev_Frame. I'm pretty new to Houdini, though have a history in coding. It's just giving me the current position.