Tweeti have seen the digital calipers that shoot the beam through your arm... is that what you are talking about? they have a pretty big margin of error. the cheapest, easiest way to get the best reading is to have an expert.. ie someone that has done it HUNDREDS of times use regular calipers and do skinfold measurements. if you have time and money, some universities offer the underwater dunk tank but its expensive and not really necessary if you ask me.