Pyzdek, T., & Keller, P. A. (2010). Six sigma handbook: A complete guide for green belts, black belts, and managers at all levels (3rd ed.). Tata mcgraw hill education.

Pyzdek, Thomas, and Paul A. Keller. Six Sigma Handbook: A Complete Guide for Green Belts, Black Belts, and Managers at All Levels. 3rd ed. New Delhi: Tata mcgraw hill education, 2010.

Pyzdek, Thomas, and Paul A. Keller. Six Sigma Handbook: A Complete Guide for Green Belts, Black Belts, and Managers at All Levels. 3rd ed. Tata mcgraw hill education, 2010.