In the sticky it states that if you require body fat % you must hold a shoe. Holding a Converse high top as JFG pointed out will actually give you a lower body fat %.
Just shitting mate, one of the most epic threads on T-Nation was all about some dude wanting to know his body fat % and for some reason he was holding a shoe. If you have several hours its a damn good read and laugh.
But read the sticky mate.