Yup, never learned what that little "x" meant back in grade-school math. Thanks for clarifying that. I'm one of those people that finds out how to make something work, but don't get me bogged down in technicalities! :)
If you don't want the 2 screens to looked compressed create a black & white mask using the media generator. Have pure black on one side and pure white on the other side. Place this at track 1, then place your media clip below on track 2 and then create a parent-child compositing relationship with these two tracks. Now add a second clip to track 3. If done correctly half of track # 2 and track # 3 will be displayed.
I used this in a home movie to show how my daughter had changed from one year to the next.