I was mystified at this. I can't imagine a way to measure weight with accelerometer that doesn't involve spinning around in circles or jumping up and down on springs.
Isn't it obvious? Drop your iPad on the floor; it won't fall exactly downwards, but will veer ever so slightly off course towards you, and the amount of displacement is proportional to your mass. Done.
Scale.com. You stand on your laptop and it tells you how much you weigh.
1) Please put your iPad on the bathroom tile and step on to it...
It wouldn't need to actually measure your weight. Bathroom scales are just there to collect dust in the corner and make people feel bad whenever they look at them.