The yarn gauge is for measuring the amount of yarn needed to rug punch or hook a rug design or pattern.
It has a handle, with a 3 inch square open area in the center. A right handed or left handed person is able to reposition the open area over a section of the design.
The open area equals 1 oz of most yarns filling in the area with ¼" loops or using the Oxford #10 regular punch needle.
1 oz = approximately 28 grams