How to Make SPC Control Chart

In this lesson, you will learn how to create a statistical process control chart.

What is a control chart?

With an spc chart, you are able to follow how your process is evolving over time. 

In most cases, the line chart type is selected for the control charts. Two lines of a lower control limit and an upper control limit are added to the chart to represent the limit values. On the control chart, you can check whether the process is in the state of statistical control. The line on the control chart must remain between these control limits.

If the values in the graph are outside the lower or upper range, it means that statistically the process is out of control. In this case, immediate steps should be taken. After that, the process should be reset.

How to create a control chart?

First, we are going to find the mean and standard deviation. To find the mean click on the Formula tab, click on More Function select Statistical and then Average from the dropdown menu. Select cells B2 to B20 and press okay.

ribbon average function

Click on the Formula tab, click on More Function select Statistical and then STDEV.S from the dropdown menu. Select cells B2 to B20 and press okay.

STDEV.S function

Select cell C1 and type "Mean (CL)" in it. Select C2 and type "=I$1". Move your mouse to the bottom right of the cell until a black plus sign appears. Drag the plus sign all the way to cell C20 to copy the mean.

Select cell D1 and type "UCL" in it. Select D2 and type "=I$1+ (I$2*3)". Move your mouse to the bottom right of the cell until a black plus sign appears. Drag the plus sign all the way to cell D20 to copy the mean.

Note: UCL= upper control limit and is mean+3 times the standard deviation

Select cell D1 and type "LCL" in it. Select E2 and type "=I$1+ (I$2*3)". Move your mouse to the bottom right of the cell until a black plus sign appears. Drag the plus sign all the way to cell E20 to copy the mean.

Note: LCL= lower control limit and is mean-3 times the standard deviation

SELECT Sample Measures, Mean(CL), LCL and UCL.

spc chart data table

Click on Insert tab, click on Line Chart and then Click on Line.

insert line chart

You have created your chart. Resize it. Remove the small black lines by double clicking on them and pressing Delete. That's it, you're done.

spc chart created chart

This is what your final chart will look like.

spc chart ready chart

Your Statistical process control chart is ready. THe process is under control as sample measures are not even close to the both lower and upper control limits.