[1] Natl Phys Lab, Div Engn & Proc Control, Teddington TW11 0LW, Middx, England
[2] NIST, Gaithersburg, MD 20899 USA
[3] AIST, Natl Metrol Inst Japan, Tsukuba, Ibaraki 3058563, Japan
[4] Natl Res Council Canada, Ottawa, ON K1A 0R6, Canada
[5] Nederlands Meetinst, Van Swinden Lab, NL-2600 AR Delft, Netherlands
[6] Phys Tech Bundesanstalt, Abbestr 2-12, D-10587 Berlin, Germany
[7] VNIIFTRI, Mendeleyevsk 141570, Moscow Region, Russia