1. ‘Process Control’, British Standard 1523, 1960 Section 2:
2. Atkinson, P.: Feedback Control Theory for Engineers, (Heineman, London 1968)
3. Young, A.J.: An Introduction to Process Control System Design, (Longmans, Harlow, Essex 1957)
4. Allen, A.J.: ‘A Wired-Logic Digital Multi-Term Controller’, 1970, M.Phil. Thesis, University of Reading, Department of Applied Physical Sciences