Trimming a flying geese block to the correct size is simple if you turn the ruler in the correct direction. This tutorial will walk you through trimming a flying geese block to 2.5" x 4.5" and it works for trimming to any size.
After making flying geese using the No Waste Method (4 at a Time), it will look like the image below. It will have little tails at the top and on the bottom two sides.
Turn the flying upside down so the wide area of the goose is at the top. Line the diagonal of the ruler to the left side of the goose on the seam between the goose and the sky.
Begin by lining up the diagonal line to the point of the top of the goose. It should line up with the line .25" away from the intended full height of the goose. Once that is in line, and sort of at the same time, line up the point of the ruler with the seam of the flying geese (noted by the red circle). Do the same with the blue circle on the other side. These should all be lined up at the same time. It is most important that the .25" at the top of the flying goose (the point shown at the bottom of the image below) is there for the seam allowance.
Make the first cut on the right of the ruler as shown here.
Make the cut across the top of the block from right to left.
Remove the ruler and turn the flying geese block over. Line up the bottom and left side of the flying geese (the sides you just trimmed) up with the size you want the flying geese to be. The bottom edges of the goose should meet the bottom corners of the block. The top point of the goose should line up with the .25" line.
Now make the cut on the right of the flying geese block. Finish by making the cut across the top from right to left.
This is what a finished and trimmed flying geese looks like.