Figure 12 shows the Box–Cox plot within the range of ±3 of the λ value. It indicates that the minimum in Ln (residual SS) occurs when λ = 0, and the long vertical green line at the centre of U-shaped curve indicates the best lambda value given by λ = 0.21. The interval is 0.08 < λ < 0.35, and the 95% confidence interval around this λ includes 0.21(Fig. 12), thus ensuring that the transformation (square root for λ = 0.5) would be helpful. For this analysis, Design Expert recommends natural log transformation (λ = 0) for the best fitting of the model. Small vertical blue line at λ = 0 shows the current transformation.