In an effort to redefine the kilogram
by tying it to a fundamental con-
stant, the mass of a single atom,
PTB metrologist Dr. Arnold Nicolaus
and colleagues have designed the
Avogadro sphere.
The single crystal silicon ball of 1 kg
is polished to 50 nm accuracy and
measured by laser interferometry in
order to determine via the Avogadro
constant the number of atoms it
consists of. Checking for dust.

[kg] ‘The KILOGRAM is the
unit of mass; it is equal to the mass
of the international prototype of the