<a href="https://en.wikipedia.org/wiki/Silicon" class="extiw" title="en:Silicon">Silicon</a> sphere used in the <a href="https://en.wikipedia.org/wiki/Avagadro_project" class="extiw" title="en:Avagadro project">Avogadro project</a> being inspected by <a href="https://en.wikipedia.org/wiki/Achim_Leistner" class="extiw" title="en:Achim Leistner">Achim Leistner</a>, master optician at the Australian Centre for Precision Optics (part of the <a href="https://en.wikipedia.org/wiki/Commonwealth_Scientific_and_Industrial_Research_Organisation" class="extiw" title="en:Commonwealth Scientific and Industrial Research Organisation">CSIRO</a>). The sphere, which has a diameter of about 93.6 mm, was cut from a <a href="https://en.wikipedia.org/wiki/Single_crystal" class="extiw" title="en:Single crystal">single crystal</a> of 99.9995% pure silicon-28 and has a mass of 1 kg. The number of atoms in the sphere has been calculated using <a href="https://en.wikipedia.org/wiki/X-ray_crystallography" class="extiw" title="en:X-ray crystallography">X-ray crystallography</a> with an uncertainty of less than 2×10<sup>-8</sup>. It is round to within one part in two million.
CSIRO ([Australian] <a href="https://en.wikipedia.org/wiki/Commonwealth_Scientific_and_Industrial_Research_Organisation" class="extiw" title="en:Commonwealth Scientific and Industrial Research Organisation">Commonwealth Scientific and Industrial Research Organisation</a>)
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