A guideline for analyzing circadian wheel-running behavior in rodents under different lighting conditions by Corinne Jud, Isabelle Schmutz, Gabriele Hampp, Henrik Oster and Urs Albrecht is an excellent article on methodology (and reasoning behind it) of basic circadian research. It was published in an online open-source journal Biological Procedures Online. I strongly recommend it to my readers.
The Reference #16 is to this post on Circadiana. Coming up on this blog in one hour!