I have one of these scales also. The comments everyone has made here are all helpful, i.e. weighing at the same time each day. The point of that is to provide a consistent level of hydration, so that all the other numbers can be compared correctly day-to-day.
You haven't wasted your money...that is simply where the technology is today for a home-based product. It can't literally measure your body fat, % muscle, water, etc...it measures an electrical signal, then correlates that with statistical data it has stored to give you a "best estimate". The manual explains these limitations, and how your current meal/hydration status affects the results.
Mine shows hydration as one of the displayed pieces of data. In the morning, it can be as low as 56%...in the evening, as high as 61%. The low hydration readings gives high body fat %, and the high hydration gives a lower bf%. While I understood that the trend was the important thing, I was kind of curious about which actually WAS closest the the real body fat. Since I had to get a dexascan (bone density measurement exam that gives a respectably accurate body fat % as a side result) anyway, I took lots of scale data on myself at various times of the day for several weeks, made a graph, then compared with the dexascan # on the day I had the test. It turned out for me, 59% hydration correlated with the correct body fat. I now know that if I get on the scale at an "inaccurate" hydration level/time of day, what percent bf to add or subtract to correlate to the 59% hydration.
I don't know if this number would work for anyone else, but I thought this was all interesting and thought I'd share.
