Sorry, my bad.
I created a picture to illustrate what I want to do:
http://oi56.tinypic.com/rwhxyv.jpg
The orange (unnamed) variable is the one I'm having difficulties with.
Var1-Var3 and the "orange" variable are recorded over time and I want to be able to see what happens with the other variables (var1-var3) when the "orange" changes.
The infinity marks are just there to point out that I want to have both Y1 and Y2 to be positive regarding vertical direction from origo.
Thank you.