hi grammy of 6, i don't think you need any special ruler. wasn't it mentioned you just measure one inch on each side of the center mark on the 4 sides and mark the line to the center??? i think?? you are just creating darts to take up the sides. i still don't get the microwaving with the bowl in it. what about boil overs? i just saw this pattern in the home-sew inc. catalog with a lid made out of oilcloth? i usually just throw a damp paper towel over my reheats to keep spatters off the microwave. I REALLY LIKE THE ICE CREAM BOWL HOLDER TIP!! lil