A guess: Two uncertain data points makes it even worse. If you can at least depend on the scale, the error is lower. I tested our old Nintendo wii (or whatever

A guess: Two uncertain data points makes it even worse. If you can at least depend on the scale, the error is lower. I tested our old Nintendo wii (or whatever it's called) balance board and so far it gives the same value every time I step on it. The value was also only 0.2 kg off from the doctors expensive scale.