Also, I
highly recommend reading the Penske shock manual. It is awesome information.
Here:
http://www.penskeshocks.com/files/Adjustable_Manual.pdf
Awesome explanation of what is happening inside a (very good) shock for compression and rebound. Also some damper tuning tips. Read it and love it. And remember not all shocks are like that inside, but it's still awesome to read.
- Andy