Scientific Instruments

Work in under way which aims to replace the "hunk of metal: kilogram standard.

One such effort is described here: http://www.csiro.au/news/PerfectKilogram.html

Peter.

So it appears there is still a physical object - now a silicon sphere. Does everybody have to make their own? I don't see the point.

I don't see how making a 'man-made' sphere out of a 'lump of crystal' is going to change the fact that the standard is still not controlled by a definite quantity! You may say that it is the amount of atoms of silicon in the sphere but by their own admittance, their spheres are not perfect. Therefore we are in the same position as before, having to use a man made object as a reference! How hard is it to define a Kilogram using constants? Do we need a physical object at all for the definition? Can we say it is equal to 'x' atoms of whatever element at a 'zero height reference point for sea level' somewhere in the world?