I put the cutting mat on one end of the dining room table and one quilt corner on the mat with the quilt smoothed on the table and overhang folded back. Generally, I measure what the border to border measurements are before I trim anything. Because I mostly use geometrics, I align the long ruler with one of the lines and then I trim. When I'm at the end of the mat, I slide the mat - realign the ruler and keep trimming. This has always worked for me.