I was winding some yarn last night. It's from a local yarn store, but you can get it online. It's great for felting--comes in lots of colours, several thicknesses, doesn't felt too quickly, and doesn't get too fuzzy when felting.
I had two balls of dark purple wound up when I noticed that one was larger than the other. Sometimes, depending on the speed setting of my electric ball winder, the balls can be tighter or looser than other times. So I thought I'd weigh them.
Ball 1 was 119g---the label gives 100g as the weight. Ball 2 was 91g! So, because I had two balls, I am ahead of the game by 10g, but that's 10%. If I had only bought the smaller skein, unknowingly, I could easily run out in a project. What if one skein had been SHORT by 19g instead of over? That's almost 20%! What if I decided to short-change them 20%?
I"m not about to complain this time, because I am in the advantage and I feel the extra 10g is a sort of 'pay off' for the aggrevation of having one ball be short. But you bet your double points I'm weighing each and every skein from there from now on....before winding them!