Buy yourself a June Tailor Half/Quarter Square Triangle ruler and you will have PERFECT ones each and every time. Cut your swatch of fabric about an inch bigger than the finished one you want (maybe less), use the ruler to mark the SEWING lines, not the cutting line. So much more accurate and easier than trying to stay 1/4 inch from the cutting line. You can use the ruler to zip cut the two apart, press it, and then square it up to a perfect half or quarter square. I had so much trouble with these before I got this ruler. Now, I don't know how I could live without it. Her rulers, including the Pro Shape Cut ruler, have laser cut lines where your rotary cutter glides down, never straying off to the side. Quick. Zip, zip, zip. The only problem with these rulers is that the cutter nicks the teardrop making it difficult to do any zip, zipping. I keep an exacto knife close by, and with the littlest of effort, smooth off the teardrop making it brand new again.