Interesting news item at Slashdot today.
Experts Suggest Replacing Definition of KilogramMakes a lot of sense. It's hard to calibrate something when the only standard is locked away in a vault. The Planck's Constant is very elegant and simple -- something that any competent lab person could whip up... Here's an image of the Kilogram Standard:
"The kilogram is the only one of the seven basic units of the international measurement system defined by a physical artifact rather than a natural phenomenon. International team of scientists suggest replacing the kilogram artifact -- a cylinder of platinum-iridium alloy about the size of a plum --with a definition based on one of two unchanging natural phenomena, either a quantity of light or the mass of a fixed number of atoms. They propose to adopt either one of two definitions for the kilogram by selecting a specific value for either the Planck constant or the Avogadro number."
Basing it off of Avogadro's number makes more sense IMNSHO. 10^23 atoms isn't _too_ far out of our direct observation range. We've become exceedingly good at making near perfect silicon crystals for some reason....