The standard kilogram kept in Paris is mysteriously losing its mass, but about 50 micrograms!
"The mystery is that they were all made of the same material, and many were made at the same time and kept under the same conditions, and yet the masses among them are slowly drifting apart," he said. "We don't really have a good hypothesis for it."
Now, 50 micrograms is actually quite big, considering that we can detect changes to a mass by single molecules. I think this strengthen the calls for a better (atomic) standard of the kilogram, much like the standard for 1 m and 1 second have been migrated to more well-defined quantities.