The one thing I do not see mentioned in quilting circles, including here, is that WOF cotton, has a naturally occurring stretch, but if you tug just inside a selvege edge, it does not stretch. As I cut my smaller squares or whatever shape, I try very hard not to turn the fabric, so my stretch will all be on the horizontal and the no stretch stays in the vertical position. If any of you can explain this better for a 'newbie' please jump in. I am not so good at making some things clear. If you do this as you cut, your corners nearly always match as if by magic.