This tool is for knitters and spinners, and is used to determine the WPI (wraps per inch) of a particular yarn. There are two ways to use this tool. The first uses the one inch notch at the top of the tool. Wrap the yarn around so it rests in the notch and then count the number of wraps. Alternatively, you can hold your yarn in front of the bars on the center of the tool, matching it to the window that has the most similar width (see second picture). Each bar is labeled with the WPI that width corresponds to, as well as the name of yarn weight.
This item is made out natural bamboo, and the one you receive may have natural variations in color, grain and texture.
Also available in light blue acrylic: http://www.etsy.com/listing/60439631/clear-blue-spinners-wpi-gauge
and Cherry wood laminate: http://www.etsy.com/listing/95523512/spinners-wpi-gauge-cherry