1. Cheaper by the dozen;Gilbreth,1948
2. ILO. Introduction to work study. 3rd ed. ILO; 1979.
3. Barnes RM. Motion and time study. 7th ed. New York: John Wiley & Sons; 1980.
4. Mundel M. Motion and time study. 6th ed. Prentice Hall; 1988.
5. Notes for NCES;Kiran,1985