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g Chart Help

A g control chart is used to monitor the time between rare events or the number between rare events. For example, you might you want to monitor the time between lost time accidents in a plant or the time between infections in a hospital. There are two options with the g control chart. One option is to track the number of units produced between events. In this case, you must enter the sample number (or date) and the number of units produced since the last event. The other option is the time between events. In this case, the dates are entered in one column and SPC for Excel calculates the time between events and puts that time in the adjacent column. The example below deals with the number of units produced between events. For more information on g control charts, please see our SPC Knowledge Base.

This page shows you how to make the g chart. The data can be downloaded at this link. This page contains the following:

Data Entry

You are monitoring the number of units a machine produces between breakdowns. The data are shown in the table below. Enter the data into a spreadsheet as shown below. The data does not have to start in cell A1. It can be anywhere on the worksheet. The data can be in columns or rows.

Creating a New g 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:

Updating the g Chart with New Data

The g 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 g Chart

You can change the current options for a u chart (e.g., changing the out of control tests) by selecting “Options” on the Updating/Options panel on the SPC for Excel Ribbon. 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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