both the scales and the handhelds run a low level electric current through your body. depending on the resistance the current subjected it, it gives an estimate on bodyfat. This is because current travels through fat differently then it does through other tissues.
you will find if you use one of these devices, they can be skewed by many different things. especially the amount of water you are retaining, and the amount of moisture on yoru skin.
I don't do this for my family, my friends, women, accolades, pride, or ego. I do it for me and no one else, its just part of who I am.