I recently completed a quilt top that was a combination of 9-patch and Snowball blocks. This is the first time that I tried squaring my blocks before sewing into rows. Loved the ease that my rows came together! However, I didn't square them properly, in that the corners of the triangles should have matched the corner of one of the 9-patches. But - it didn't. I have hopefully attached pictures to help.
What I did. I lined up the diagonal across my 9-patches. Couldn't figure out what measurement to line up on a vertical seam, gave up on that. Ending size of my block - 6-1/4 inches (technically that would be 5-3/4 with seam allowances for the outside edges added in). I made sure the diagonal was correct, the 1-1 on the square ruler was in the top right hand corner, and that the bottom and left edges were over the 6-1/4 inch lines on the ruler (wanted to take off roughly equally on all sides). Did the same on the Snowball blocks.
I believe that I needed to line up on a vertical seam - but in doing that it, wherever I put it, it seemed I would be taking a lot more off one side than the other.
What should I do the next time?