Understanding Body Fat Measurement: Calipers & Hydration

Question
A few friends of mine are having a wager over who can lose the most fat. I will be using calipers to determine the winner.
What I want to know if there is anything they can do to throw it off, suck as dehydration and "sucking it in". If they try anything is there any way I can tell?

Answer
Eric,

With callipers, the "sucking it in" thing should not affect the body fat percent measurement. Theoretically, hydration can be detected, but it'd require more sophisticated tools like impedance, underwater weighing, etc.

However, you can try to put all participants in equal condition by equally and properly hydrating everyone on test days.

You might also want to double-check the fat percent of your friends by using different methods including tape measurements:

http://bantadiet.com/banta/?page_id=21

Tanya Zilberter