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My wife and I are also slightly obsessive fitbit'ers.

We use fitbit's aria smart scale and like to use trendweight.com to track our weight trends. I've lost over 15 lbs over 6% body fat, and my wife has lost more as well.

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How does the scale measure BF%? My impression was that calipers were really the only way to do it accurately without expensive equipment.

A number of consumer scales use some form of electrical pulse timing to determine the composition of tissue in the feet, which is extrapolated for the body. For these results to be meaningful, you have to be very consistent with your hydration before you use the scale.

After measuring daily for about two months with such a scale (in the mornings after going to the toilet and before drinking anything, so I assume my hydration should be somewhat consistent) I see a clear downward trend (in line with my weight loss), but the actual values that are measured don’t seem to be very exact, probably about ±3% around the imaginary trend line.

Those measurements seem to be good for finding a trend, but not for finding the absolute value.

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