References
- Nath, N. G. & Choudhury, A. K., J. Instn Telecom. Engrs, 15 (12) (1969), 809–814.
- Kuo, B. C., Automatic Control System, second Edition (Prentice-Hall, New Delhi), 1967.
- Nath, N. G. & Choudhury, A. K., Trans. IEEE on Automatic Control, AC-11 (2) (1966), 320.