The best way I could think of to actually use the iPad for this would be have a person lay his arm (including wrist) on it. The iPad can use the touch sensitive

The best way I could think of to actually use the iPad for this would be have a person lay his arm (including wrist) on it. The iPad can use the touch sensitive surface to measure how thick his wrist is and how thick his arm is, and then guess his weight. Using an accelerometer would likely be a worse user experience than just stepping on a scale, but a system where the iPad actually measures your body fat could be easier to use. However, it will likely not be very accurate. Perhaps if one were to set a reference weight at the start, and it just measures delta using the touch screen? Using the accel, a possibility is to see how close a person can swing the iPad towards his body. I assume that this would change dependent on the amount of fat around his arms. A common place people gather fat is on their thighs - thin people often have space between the legs and heavier people not as much. Also a possibility, even if a not very clever one.