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This is one of the two most perfect spheres ever. Exactly one kilogram—Imperial units be damned forever—smooth to the nearest 0.0000000003 meter (1.18110236 × 10-8 inches), and round to within 0.00000005 meters (1.96850394 × 10-6 inches).
They were made using silicon by metrologists from the by Australia's Commonwealth Scientific and Industrial Research Organization. [Makezine]
