Acknowledgements

The author is grateful to Dr. H. Bachmair, Dr. J. Melcher and Dr. M. Klonz (PTB), to Dr. A. Koffman, Dr. J. Kinnard and Dr. Y. Wang (NIST), to Dr. A. Tarlowski (GUM) for their constant support and very useful advice during the project development, to Dr. H. Hall for his very helpful criticism and advice during paper consideration. I would like to specially acknowledge my teacher F. B. Grinevich and colleagues A. Lameko and D. Surdu, who have spent a great part of their life realizing variational ideas.
