Creative Grids Quick Trim Ruler by Rachel Cross & Karen Montgomery.
Ruler is 3 1/2" x 12 1/2". By using the holes drilled in the center of the ruler you can draw circles from 2" to 22" in diameter, and every half-inch in between. Use the 45 degree angle lines that cross at 1/4" to trim points from half-square triangles and flying geese.
Creative grifd rulers also have Embedded Gripper Strips that hold fabric while cutting.
