1. Aalto M. I. and Ehnholm G. J. (1973) A self-balancing resistance bridge. J. Phys. E.: Sci. Instrum.
6, 614 - 8.
2. Agar J. (1969) Frequency-modulating trans- ducers Radio Electron. Engng
38, 89 - 97.
3. Allgeier R. L. and Reger J. A. (1968) New automatic dewpoint atmosphere control. Proc. 18th ISA Iron and Steel Instrumentation Symp. ( Pittsburgh: ISA ) pp. 105–121.
4. Auckland D. W. and Hawke J. R. (1978) A thread-tension transducer using torque-balance about the axis of a motor. Proc. Transducer ‘78 Conf. ( Tavistock: Trident International Exhibitions).
5. Black H. S. (1934) Stabilised feedback amplifier. Bell Syst. Tech. J.
13, 1.