(This post was inspired by a discussion on SamuraiKnit's blog about Western vs. Eastern vs. Combined knitting)
I've been seeing a lot of confusion on the knitterwebs about whether we wrap our yarn clockwise our counter-clockwise for knit and purl stitches. This confusion stems in part from popular books like "Stitch and Bitch", which a lot of knitters (including me) learned many techniques from; when I look at those tiny little diagrams in books and read "wrap the yarn counter-clockwise," I can't imagine how anyone DOESN'T get confused.
From my perspective, as I'm knitting, knit stitches are wrapped clockwise - under the needle from my right-hand-side to my left-hand-side, then over the needle the other way. But, in relation to the tip of the needle (and who takes that perspective?), the yarn is wrapped counter-clockwise! See, CCW from the perspective of the tip of the needle is CW when looked at the other way.
Let's complicate things further: when I turn the needle around to point towards me(i.e., to purl), I wrap the yarn counter-clockwise: from my right-hand-side over the needle to my left hand side. If you think about it, the yarn is wrapped around the needle exactly the same direction each time, but it's often described differently in books. It seems like this confusion of terms causes some new knitters to start knitting Combined without even realizing it, since they're "following the directions in the book."
Thankfully, scientists and mathematicians have faced the same problems, and developed standard solutions for describing the direction of rotation. Anyone who's taken a physics course should recognize the Right-Hand Rule, which is actually more like a convention. They needed a way to communicate the direction of rotation without all this, "well, it looks clockwise to ME - it's going from your top LEFT to your bottom RIGHT" and so on. For example, a wire charged with electricity also produces a magnetic field around the wire. Scientists who study that field take the convention that the magnetic field curls "right-handedly" around the wire, meaning that if you point your thumb in the direction of the flowing current, your fingers curl around in the direction of the magnetic field.
So lets get back to knitting. Point your right thumb along the needle from the base to the tip (the one that you knit with, if you're using dpns) and think about making a knit stitch. Look, your fingers curl around in the direction of the wrapped yarn. (if you knit Western style) Now do the same with a purl stitch - it's "right-handed," too.