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z-mR Chart Help

z-mR charts are used to monitor short production runs. This allows you to plot different products on the same chart. The “z” values for each product are plotted on the z chart. z is defined as the following:


You may use the product average in place of the nominal value. The moving range chart plots the range between consecutive z values.

Data Entry

The data are entered into a worksheet as shown below (using the first part of the data in the example workbook). The data does not have to start in A1. It can be anywhere on the worksheet. The data can be in rows or columns. This example has the data in columns since the sample identifiers are in a single column. In the example below, the sample numbers are in one column, the product identifiers are in one column and the sample results (values) are in one column. With the z-mR chart, you have the option of running the chart using the nominal for the product or the average for the product. If you use the nominal, the nominal values must be entered in one column. If you select the average option, the software calculates the average to use for each product. With the average option, you do not need the column with the nominal values.

Creating a New z-mR

The options are:

Options for the z-mR chart

On the input screen for the z-mR 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.

The options are explained 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.

These options include:

Note: only four tests apply to the mR chart:

Titles and Formats

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

The options include:

Enter Product Statistics Option

You have the option to enter the average and sigma metrics for each product. If entered, these will be used in place of the calculated values. To use this option, you must enter the product metrics in the worksheet before you make the z-MR chart. The data entry must in the following form:

When the z-mR chart input screen is shown, select “Show Options” and then select “Enter Product Statistics”. The input screen below is shown.

Select the “Use the range below for the product statistics” and then select the range on the worksheet containing the information. Select OK. The program will use the entered values in place of the calculated metrics.

Box-Cox Transformation

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

The options are:


Chart Location

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

The options are:


Updating the z-mR Chart with New Data

The z-mR 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 z-mR Chart

You can change the current options for a z-mR 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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