The Gauge Ruler by Ann Budd Knits is a clear plastic ruler with white and black markings of knitted stitches. The gauge measures 11 gauges from 4 stitches per inch to 9 stitches per inch in 0.5 stitches/inch increments.
To use the ruler just move it across your knitted fabric until the images of the stitches on the ruler match the stitches in your knitting. If you need to achieve more stitches per inch you will want to move down to a smaller needle size. If you need to achieve fewer stitches per inch, you will want to swatch with larger needles. For the most accurate measurements, you will want to measure the number of stitches over 4" of knitting.
The ruler measures 9" long x 2" wide.