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EWMA Chart Help

The Exponentially Weight Moving Average (EWMA) control chart provides a method of detecting shifts from the process target. It does this by providing different weights to past data points. The EWMA monitors the variation in a subgroup average or individual value.

Data Entry

A sample from a process stream is pulled once an hour and tested for a certain product characteristic, X. It is very important to keep X as close to the average (or a target value) as possible. You enter the data are entered into a worksheet as shown below The data does not have to start in A1. It can be anywhere on the spreadsheet. The data can be in rows or in columns. Note: this example uses individual values, but you may use subgroups as well.

Creating a New EWMA Chart

This is all that is needed to make the chart. If you select OK at this point, the software will generate the control chart using the default options. Simple and quick.

The options on the input screen are:

Options for the EWMA chart

On the input screen for the chart, there is a button labeled “Show Options”. If you select that button, the input screen will show the options available for the chart. It is not required to select any of these options.

Each option is described below.

Out of Control Tests

If you select the Out of Control Tests, the input screen, Tests for Out of Control Points, is displayed below.

There is one out of control test:

Control Limit Options

f you select the “Control Limit Options” button, the following is displayed.

The options include:

Titles and Formats

If you select the “Title and Formats” button, the following screen is displayed:

The options include:

Manual Control Limits

If you select the “Enter Average & Sigma” button, the following screen is displayed:

The options include:

If entered, the program uses these values in place of the calculated values.

Chart Location

If you select the “Chart Location” button, the following screen is displayed.

The options are:


Box-Cox Transformation

Selecting the “Box-Cox Transformation” button displays the following screen:

The options are:


Updating the EWMA Chart with New Data

The EWMA chart can be easily updated with new data after it has been added to the spreadsheet. Please see Updating Control Charts with New Data to see how the software finds the new data and updates the chart.

Changing the Options for the EWMA Chart

You can change the current options for an EWMA chart (e.g., adding a Box-Cox transformation) by selecting “Options” on the Updating/Options panel on the SPC for Excel Ribbon.

The list of available charts in the workbook will be displayed. Select the chart you want to change options for. The input screen for that chart will be shown and changes can be made. See Changing Chart Options for more information

In addition, once a control chart is made, there are numerous actions you can take on the chart including splitting control limits, removing points from the calculations, adding comments, selecting the range on which to base control limits, etc. Please see Control Chart Actions for details.

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