[ 비 특허 문헌 1 ] Wallance . J . Hopp , Mark . L . Spreaman , Variability Basics , Factory Physics , p 248 - 286 , Irwin Professional Pub , 1995 [ 비 특허 문헌 2 ] Youichi Nonaka , Attila Lengyel , Kouichi Sugimoto , Monitoring Variance in Manufacturing System Performance , 40 th CIRP International Seminar on Manufacturing Systems , 2007