How Do I Create Control Charts in Excel?
A control chart is a useful tool for studying how processes or other data changes over time. The chart consists of four lines -- the data, a straight line representing the average, as well as an upper control limit and a lower control limit.
Open a blank Excel worksheet. Type the name you want to use for your data in cell **B1** and then enter the data for your chart in that column. In our example, 12 numbers are entered in cells **B2** through **B13**.
Select a blank cell below your data in column **B**. Click the **Formula** tab and then click the small **Arrow** beside the **AutoSum** button. Select **Average** from the drop-down menu. Highlight the cells containing the data and press **Enter**.
Select the blank cell beneath the cell used to calculate the data average. In our example, this is cell **B16**. Click the small **Arrow** beside the **AutoSum** button again. This time select **More Functions**. Click **STDEV** in the window that opens, highlight the cells containing the data and press **Enter.**
Type **Average** in cell **C1** and then click cell **C2**. Type **=** and then click the cell containing the average. Insert a **$** between the column letter and row number and then press **Enter**. In our example, the formula is **=B$15**.
Select cell **C2** and press **Ctrl-C** to copy it. Drag the cursor over the blank cells in column C that have a value beside them and then press **Ctrl-V** to fils each cell with the average. When you plot the control chart, having these cells filled with the same number gives you a straight average line.
Type **UCL** in cell **D1** to specify the Upper Control Limit. The UCL is calculated by adding the average to 3 times the standard deviation. Type the following formula into this cell, replacing "B15" and "B16" with cells containing your average and your standard deviation: **=B15 + (B16*3)**Insert a **$** between the cell and row for each cell and then press **Enter**. Your final formula in this cell should look like this: **=B$15 + (B$16*3)**
Type **LCL** in cell **E1** for the Lower Control Limit. The LCL subtracts 3 times the standard deviation from the average: **=B15 - (B16*3)**Insert a **$** between the cell and row for each cell and press **Enter**. The final formula in this cell looks like this: **=B$15 - (B$16*3)**
Copy the cells containing the UCL and LCL values and paste them into the cells below them. This will give you straight lines for both the UCL and LCL values in the control chart.Highlight the cells containing the Average, UCL and LCL data.
Click the **Insert** tab and click the **Line Chart** icon. From the drop-down menu, select the first line chart that appears.
Click the **Chart Title** at the top of the line chart and replace it with **Control Chart**. If you want to change the appearance of your chart, click the **Style** icon beside the chart and select a new style.