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CUSUM Chart Help

The Cumulative Sum (CUSUM) chart examines the deviations of results from a target value to see if the process is operating on target. The cumulative sum is the sum of these deviations over successive samples. The first step is to determine what shift from the target you want to detect quickly. This shift is usually one standard deviation of the parameter being plotted. Results near the target value are considered to be an indication that the process is operating on target. These result in a subtraction from the cumulative sum unless it is already 0. Results that are beyond a certain value (which depends on the shift you want to detect), are considered evidence that the process is not operating on target and these are added to the cumulative sum. If the cumulative sum exceeds the control limit, an out of control situation occurs.

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 CUSUM Chart

The target for the process is 30. That value is entered into the as shown below. Note: you also have the option to use the average in place of the target (see options below)>

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 CUSUM chart

On the input screen for the chart, there is a button labelled “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:

Enter Sigma

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

The options include:

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 Chart/Changing Options/Chart Actions

You can easily update the CUSUM chart with new data. You can also change the existing options used to make the chart. You can also take numerous actions on the existing chart such as deleting points from the calculations, splitting control limits, etc. Please see the links below for more information.

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