For the determination of the count of yarn, it is necessary to determine the weight of a known length of the yarn. For taking out known lengths of yarns, a wrap-reel is used. The length of yarn reeled off depends upon the count system used. One of the most important requirements for a spinner is to maintain the average count and count variation within control.
Read more: http://textilelearner.blogspot.com/2012/05/yarn-numbering-system-yarn-count-direct.html#ixzz4BMCeDcOc