If you are pulling a yarn out of a cylindrical package how can you measure how much tension you are applying to pull the yarn?

If you wanted to know how many ounces or pounds you are applying you can use a spring scale that has a hook on the end of it.

Here is a web site that has various spring scales for sale. There are other spring scales that have different ranges of force that can be used.

http://www.arborsci.com/Products_Pages/Measurement/SpringScales.aspx