An injection molding machine for plastic bottles has four molding heads. The outside diameter of the bottle is an important measure of process performance. The following are histograms of the outside diameters for 40 samples from each of the four heads. The values plotted are the difference between the outside diameter and the target value. a) What conclusions can be made about the output from these 4 heads based upon these histograms?

Histogram of Head 1 Histogram of Head 2 18. 14. 16- 12. 14- 10- 10- 0.04 O.CH 0.12 0.04 Difference from Target Difference from Target Histogram of Head 3 Histogram of Head 4 bi 14 4 -004 0.00 D.12 -0.04 0.00 008 0.12 Difference from Target Difference from Target