"Le Grand K" refers to the platinum-iridium cylinder which has been maintained since 1879 under triple lock and key at the International Bureau of Weights and Measures in Paris. Its mass is the official definition of one kilogram and is used as the standard for kilograms across the world. Every 40 years, it is pulled out of storage, washed with alcohol, lightly polished, and compared to 80 other kilogram standards retrieved from laboratories from other countries in order to confirm that everyone is using the same kilogram.
Unfortunately, Le Grand K at its most recent check-up in 1988 was found to be light by 0.05 milligrams, which is about the mass of a grain of sand. Among the theories for an explanation of this phenomenon is that the 80 other standards are handled more frequently and have accumulated contaminants or that Le Grand K had some air molecules escape from the metal over the years.
Many other units of measurements are based on the kilogram, so if Le Grand K is flawed, a lot of other stuff may be also. When dealing with items as small as microchips, the slightest inaccuracy could have major consequences, none of them pleasant. Physicists believe that this will be a serious problem in industry in the next few years and are groping for a better way of defining the standard kilogram.
To learn more about the dilemma of Le Grand K, check out this site from mental_floss, one of my favorite magazines.
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