Scales are calibrated differently, so you can get a different reading on each one. The type of flooring can effect a scale too. Pick one scale as your "official" scale to get the most accurate gauge of weight loss. To check for accuracy, put an object you know the weight of on the scale (like a 5lb weight) and see how accurate it is. You should also weigh in the same clothes, same time,(morning is best before eating and after going to the bathroom).