I had one those last summer(Tanita Ironman) and it said I was 175lbs @ 22~24% bf.... yeah right... looking in the mirror is more acurate than these things when my ab and rib striations are clearly visible...LMAO @ that scale so I took it back!!! Total waste of $$$
They have a +/- 8% flucuation. Read the manual and then you'll see it's a waste. Have someone caliper you @ your gym; prob. a lot more accurate.
The manual also stated that how much water you drank will impact the reading, so if you're dehydrated it will say you have more bf%