mrbluze writes: The standard kilogram weights which are used by countries around the world for calibration have variably increased in mass by tens of micrograms. This poses a threat to the precision and comparability of measurements in science, engineering and trade. The problem is due to surface contamination, but a safe method of cleaning the weights has only recently been devised by the use of ozone and ultraviolet light. Link to Original Source
"The fundamental principle of science, the definition almost, is this: the
sole test of the validity of any idea is experiment."
-- Richard P. Feynman