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like these ones?
http://www.amazon.co.uk/gp/product/B000BB0BVG?redirect=true&ref_=s9_simh_gw_p364_d0_i1my scales are set up but simply take a my height and weight and put an assumption in there about how much is likely to be fat, presumably based on a non athlete, as given that I can see the outline of my abdominal muscles, I find it unrealistic that I'm 25% fat, but I'd like to know where I am as I suspect that its a better way of both setting a realistic weight goal.
You need to set the scales up with your details otherwise they're way off.
They all estimate based on parameters you start with. Tanita are tested against other measurement tech (DEXA etc) and the go to brand for accurate scales.