I lay mine on the cutting table and run my largest ruler along the edge....I ALWAYS leave half the ruler on the already cut edge....to line it up. If it has a border, I use the seam and adjust until the seam is on a line -- whether it's the opposite side of the ruler or a line in the ruler. ALWAYS ALWAYS make sure the quilt is not falling over any edge of the table. This pulls the quilt out of alignment. It may LOOK straight, but more than likely, it's not.