I thought that in Britain each scale used commercially, as in charging money for the weight of the item weighed, was required to have a current certificate of test, renewed every five years, issued by the Department of Weights and Measures. I'd ask to see that certificate, determine who is responsible for the scale and make as much noise and trouble as possible. It's usually much more fun doing that than making your flight. The legislation must be the same throughout Europe and in any event, a misreading scale is a flagrant breach of your human rights.