Boy oh boy, we can really tell those who paid attention in their physics
classes!

I wrote a lengthy piece on this back in 1997, search the archive on CV
and pencil if you want the full version. Here's the brass tacks:

The preventative maintenance procedure to lengthen the service of CVs is
to swap the entire axle, intact with CV's, from one side of the van to
the other. By so doing, you reverse the angle of thrust, and thus begin
wearing on the opposite wear surface in the large and small groove.

A couple of folks in this thread have described pretty effective means
of envisioning this, but my favorite is with a pencil. Grip the eraser
end in your left hand, and the pointy end in your remaining hand.
Imagine that your left hard is the transmission flange, and rotate the
pencil as if you are driving and the pencil is the passenger-side  half
axle, noting the direction of rotation.

Watch the brand name of the pencil come around, is it upside down or
right side up???

Now take the erasure in you right hand, and repeat the experiment, the
pencil now representing you driver's side half axle. Do you get it now?

No? Well there is no hope for you then. Check your speedometer, you may
be driving in Kph.

G. Matthew Bulley
Divine Emporer of the
VW Heat, Rust, Noise Web Page
http://www.bulley-hewlett.com/VWindex/
Owner of too many VW's to mention
Mount Olive, NC