The Capability Histogram is located in the upper right corner of the Capability Sixpack - Between/Within.

Use the capability histogram to assess whether the data are normally distributed. The capability histogram consists of:

·    Between/Within and overall curves that are superimposed on the histogram. The between/within and overall curves are normal density functions using the process mean and different variances. The between/within curve uses the within and between subgroup variance, while the overall curve uses the overall sample variance.

·    Bars, which represent the measurements for the whole process. With small sample sizes, it may be difficult to assess normality using a histogram.

Assess the normality of the data by comparing the curve to the bars. A normal distribution is symmetric and bell-shaped. With small sample sizes, it can be difficult to assess normality with a histogram. The coating data appear approximately normal.

Examine the curves to see how closely they follow each other. A substantial difference between the B/W and overall curves may indicate that the process is out of control.

For the piston data, the B/W and overall curves are approximately aligned. Therefore, the data appear to follow the normal curve.