Apart from development testing and a few extreme conditions, a servo system spends most of its life dealing with small movements. These may be so small as to fall into the region of threshold conditions, where non-linearities become of the same order as command signals. In this paper an attempt is made to bring together some of the known facts associated with this region and the techniques used for improvement. It is hoped that this will stimulate further discussion in this interesting and rewarding topic.
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