I think Jesus had in mind something a little faster than 50 micrograms in a century.
50 micrograms from 1 Kilogram within 100 years is very significant indeed.
However there are other factors that needs to be investigated as well such as: 1) the accuracy of the scales 2) possible contamination or erosion of the specimen kept in storage 3) possible fraud, where the item was either stolen, switched or never properly made to start with 4) outside influences (possible gravimetric influences) affecting the weighing.