this is the method they used for Summer in the park quilt. I started making that quilt you do not need a special ruler.
http://www.youtube.com/watch?v=vOWSp0mTTqE I believe she tells you how to use a normal ruler. Remember that she gives the incorrect measurement when the strips were sewn together, she says 4 1/4" lol it's actually 4 1/2"...
In the video you watched they tell you to refer back to the video link I have included...