Before using the scale, you have to tell it how much you weigh. Since the entire premise of the product is that it tracks your weight automatically, this doesn't make sense. Ideally, entering your weight wouldn't be anywhere in the process. If the system must have it, an option of getting on the scale for the initial measurement should be presented.
A minor annoyance, to be sure, but that's true of most problems in user experience design.
1. Fitbit Aria - The bathroom scale with Wi-Fi. It connects to the fitbit.com web site to track the weight and BMI for your entire family. Except for kids and folks with pacemakers. I don't have a pacemaker, but it freaks me out a little that you aren't supposed to the Aria if you have one.