The Marti Michell ruler differs from most other 60 degree rulers in that the measurements on her ruler run along the side of the ruler, not from the center of the base to the top. When you are lining up her ruler on the 8.5" line it is actually going to make a triangle that is much smaller than you need. It would be better to use another ruler.
Here's the explanation from her site -
http://www.frommarti.com/60deg.shtml