OT: Can anyone recommend a good pairs trading primer?

["cby" <cby1@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>]

Hello,

Can anyone recommend a good (stock) pairs trading primer? Most of what 
I've found look to be expensive and *very* heavy on the math (I know 
there's gonna be math, but... ;-).

And if anyone has done work on pairs trading in AFL, and is willing to 
share, I am of course all ears ;-). 

Thanks,
Chris