Figure 2: Response surface plot for MRR: (a) factor plot, (b) factor plot, (c) factor plot, (d) contour plot between and , ((e) and (f)) interactions plot between and , (g) contour plot between and , ((h) and (i)) interactions plot between and , (j) normal plot of residuals, (k) residuals versus predicted values, and (l) predicted versus actual values.