Blinkmanpp This is second time tonight I have posted this I hope it helps. It was originally posted on Any Sock KAL 2.
Go to Bass Pro Shops
and buy a fishing line counter. This is the expensive model $12.99. There is a cheaper version, $10.99, the cheaper model is electric and the expensive is mechanical. I have the expensive model, the batteries aren't dead when you need it.
I would, haven't done two at once yet, wind from the skein through the line counter to a yarn winder. This gives the total yardage. Take the new ball and repeat the process for half the yarn. I find the top to a 50 CD spindle to be nice to hold balls of yarn when I rewind from them especially if winding from the outside.
At about $15 US for the line counter and shipping I think it was a good investment.