ok, a pic is worth a thousand words in this case.
the triangle measures 5.5 inches along the base and 8.5 inches tall.
with this template its best to use the gridded template material. here's a link to what i'm talking about.
http://www.ezquilt.com/products/plastics/gridpak.htm
you want to mark the base of the triangle a 1/4 inch below the 1st inch grid mark (see pic) extend this line 5.5 inches to form the base.
now to mark the top of the triangle. make a line 1/4 above the 2nd to last inch mark of the gridded template material. the line intersects at the 3 inch vertical line (see pic) and extends horizontally to the first dashed line on each side or 1/8 inch to each side. see pic of the top section of the triangle.
now draw a diagonal line from the top to the one inch mark on the template plastic on each side.
now draw a line from the one inch mark lines to the bottom base line of the triangle - this is snipping off the corners (aka the dog ears). you're making a blunt edge instead of having a fine point template (see pic)
then draw a line on the inside 1/4 inch in to divide the seam allowance from the triangle edge. see photo.
now you can mark the inside of the template 1, 2, 3, 4, 5, 6, 7, 8 down the center line - these measurements indicate inches from edge to edge.
when you're done marking everything up on the template - just cut it out and your good to go.
you could then attach this to hard plastic to make a more stable template or just use it with your standard rulers.