Messed up weight stats: New scale underweighing by 3kg

Hi... I've been studying for 5 months abroad. One of the first things I did there was buy a scale to monitor my weight loss. However, now that I'm back in my home country, and using my regular scale again, I was shocked to find that the scale I was using abroad was underweighing me by 3kg (I did a test with another scale just to check)... When I left my study country, the scale was telling me 51 kg (which was my goal weight) but alas the scales in my home country are weighing me at 54kg. What annoys me most now are that the stats I have been tracking and recording in the past 5 months are therefore all wrong! Otherwise, I'm quite happy with the way I am and continuing my efforts. Just a bit shocked that's all.