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The Thompson-Lampard calculable cross-capacitor is used at the Physics and Engineering Laboratory (PEL) for the derivation of the ohm. A description of a calculable capacitor capable of determining the value of a 0.5 pF capacitor with an uncertainty of 2.2 parts in lo8 is given. A detailed model of the frequency dependence of calculable capacitors has been developed. This model is used to specifically derive the frequency correction for the PEL calculable capacitor. The model predicts a departure from a simple square-law frequency dependence of the correction and explains the observed frequencydependent non-linearity of the capacitor. The model is also used to investigate the effect of changing the length and diameter of the capacitor and the significance of the use of ferromagnetic materials is also investigated.

A comparison of capacitance at 10 pF was conducted between thirteen participating laboratories from the Asia-Pacific region. Measurements were made between 2004 and 2006. The behaviour of the travelling artefact was consistent with a steady linear drift at a rate of approximately 0.1 µF/F per year. Despite the wide range of capabilities within the region, the results showed good agreement between all but one of the participating laboratories.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

A simple traceable mains-frequency current transformer ratio build-up scheme has been developed which enables calibration of ratios from 5 A : 5 A to 500 A : 5 A with uncertainties of 0.05 pAIA and 0.05 pad.The build-up is based on series-parallel interchange of primary windings of two-stage transformers with magnetically shielded second stages.