bought all the 1/4 inch gadgets/feet to help me insure that I sew a 1/4 inch. Still no luck.
If some of you seams are 1/4 in spots and different size in other spots then that will cause waves and curves when pressed. If your seam has to be constant width all the way from start to finish. The fabric should be starched and iron before cutting if you want to use starch. The Stripology ruler is great so I doubt that is your problem unless you are using it wrong. Cut paper instead of fabric with the ruler to see if your problem is in your fold.