Frequency histograms are the ultimate tool for visualizing process capability. The height of each bar on a histogram shows how often a given range of values occurs in our data. Histograms can be made manually, but there are a number of software tools available to get the job done easily.
Consider each bar on a histogram a “bucket” that is assigned to a given range of values, with the height of each bar representing a number of data points that fall into each “bucket.”
The following histogram shows 50 tire pressure readings from an outgoing product audit at a motorcycle factory:
Note that the x-axis is divided into “buckets” or cells, and the y-axis shows how many data points fall inside each bucket:
Finally, we can add specification limits to graphically show how capable the process is: