1. van Assendelft, O. W. Nature 362, 388 (1993).
2. Le Système International d'Unités (SI) The International System of Units (SI) 6th edn (Bureau International des Poids et Mesures, Sevres, 1991). [ISBN 92-822-2112-1].
3. Quantities and Units. Pt O. General principles ISO 31.0 International Organization for Standardization 1992 [Obtainable from national standardization institutions.]
4. SI Units and Recommendations for the Use of their Multiples and of Certain Other Units ISO/DIS 1000 (International Organization for Standardization, 1990) [Obtainable from national standardization institutions.]
5. Asten, E. L. Nature 345, 506 (1990).