You place the gauge on the knitting and use the slider to measure off 10 stitches. The slider points to a number indicating the number of stitches per inch.
I decided to cast on 88 stitches for my calorimetry which I figured would measure 19 - 20 inches when finished. I followed the rest of the instructions on the pattern, knitting the number of rows indicated and it turned out perfectly!
I purchased a skein of Taos yarn to knit another one. This is an earth toned wool with twists of other colors which should be a different effect than the self striping colors of the Noro.
This project would be a great gift! It knits quickly and everyone seems to love it!