1. M. S. Hämäläinen and R. S. Ilmoniemi. Preprint TKK-F-A559, Helsinki University of Technology (1984).
2. A. A. Ioannides, In: Advances in Electronics and Electron Physics Supplement 19, Inverse Problems: An Interdisciplinary Study,pp 205–216, P. C. Sabatier ed, Academic Press, Orlando (1987).
3. L. Narici, I. Modena, M. Peresson, V. Pizzella, G. L. Romani and G. Torrioli, In: Biomagnetism 1987, pp 134–137 K. Atsumi, M. Kotani, S. Ueno, T. Katila and S. J. Williamson eds,Tokyo Denki University Press, Tokyo 1988.
4. R. J. Ilmoniemi, S. J. Williamson and W. E. Hostetler, In: Biomagnetism 1987, pp 182–185 K. Atsumi, M. Kotani, S. Ueno, T. Katila and S. J. Williamson eds,Tokyo Denki University Press Tokyo 1988.
5. C. J. S. Clarke and B. S. Janday, In Inverse Problems 5 (1989) 483–500.