DiStefano, J., Stubberud, A., Williams, I. (2011) . Introduction, p4, chl, Schaum's Outline of Feedback and Control Systems, Second Edition (Schaum's Outline Series), McGraw-Hill.
Krackov, S. K. (2010). Giving Feedback, Ch 47, In A practical guide for medical teachers, 3rd ed. Dent JA and Harden RM eds, Churchill Livingstone.