During this unit, you'll be making calculations based on data from an example project. In order to follow the exercise more easily, it is recommended that you print out a sample chart to work on. Clicking on the following link will open a new window with a page containing a sample chart which you can print out and fill in as you go.
The project, the production of training materials to support the introduction of Information Technology into the company concerned, is made up of a series of separate modules. As with any multi-phase project, therefore, we are dealing with a series of separate episodes, each of differing complexity but all of equal importance.
In this example, the Chart is being used for two main reasons:
As each module in the Course is different, each will naturally take a different amount of time to develop. Also, data will become available at irregular intervals (ie. when the module is completed) and in low volume (1 measurement per module).
If we were to use a mean and range chart with subgroups of size 4, we would only have five points on the chart by the time the first twenty modules had been completed, and that could take weeks. Furthermore, there is no way of knowing whether the first four modules that are completed are sufficiently homogeneous to justify calling them a rational subgroup.
For a project like this, an XmR chart is the best choice.