Intercomparison of silicon samples from the Avogadro project

The NIST lattice comparator currently assesses lattice parameter differences among carefully prepared samples of monocrystalline silicon with a level of imprecision near 10/sup -8/. This instrument has recently been used to effect intercomparisons among samples from laboratories currently engaged in direct optical measurements of such lattice period. Results reported here assist in global estimates of the current state of the art of these determinations.