This is a balance scale that is used to determine how many yards of a yarn are in one pound. It’s great for letting you know how much yarn you have on an unmarked cone or skein. Place a length of yarn in the “V” on the balance arm, and cut off pieces until the arm balances. Measure the length of yarn in inches. Multiply the number of inches (and fractions) by 100 for the approximate number of yards in a pound. Measure carefully because you multiply your measurement and your error by 100.
This tip can be found in Book 1: “Winding a Warp and Using a Paddle” and “Weaving for Beginners”