Scales are all calibrated differently and the flooring can effect the scale (should be on a hard flat surface). So many people may weigh on the gym scales and they may need to be calibrated often but aren't. Pick one as your "official" scale to accurately gauge your weight loss. Weigh the same day, same time, same clothes, etc. for the most accurate reading. I like in the morning before eating or drinking anything and after going to the bathroom. I have weighed in at 5am and then weighed at 7am and been lighter at 7am. Scales will fluctuate all day long.