How much is WPI realy used?

Tomorrow I will be ordering an oak swift from Hornshaw Wood Works this one here and noticed that for about $7 he has this nice WPI tool. In the future I will be ordering a Lendrum wheel and spinning my own yarn and was wondering how much do you really use WPI when making yarn.
ThanX as [U]ALWAYS[/U]

If you’re spinning your own yarn it would be really useful to know what wpi the yarn turns out. I don’t know that you really need a special tool, you can wrap the yarn around a pencil or needle and count the wraps in an inch, or use a ruler which has a convenient measure on it.

Does circumference matter?

When measuring wpi? Nope, it’s to measure the thickness of the yarn, so wrapping around anything - flat, square, round - where you can measure how many strands per inch works.

I only used the wpi measuring tool when I was skeining up yarns for sale or using a yarn for a project.

What I like much better is a spinner’s control card & yarn guage. I keep it on my wheel so I can make sure I’m spinning a consistant wpi.