I learned years ago when sewing blocks together made by different quilters for a charity donation that all 1/4" are different. No 2 blocks measured the same. Some I had to remove fabric when squaring up some I took apart and restitched and others had to have a narrow border. It was very frustrating. I've also learned to never use the lines on a cutting mat for accurate measuring and cutting. I've measured several of mine and had as much as 3/4" difference by the time I got to the end of the mat. Now I only use the lines to line up straight of grain.