Loads of choices here.
As Barbara says, to remove a point from the graph you can use the data options.
This will remove the point from the chart.
alternatives are to * the data point out in the worksheet. My preference here is to create a new data column, that way keeping the original data.
To keep the data point on the graph but exclude the point in the calculations you can use I-MR chart options and the estimate tab will allow you to exclude/include (points on an individual chart, subgroups on xbar-r) from the calculations.
The Assistant control charts also allow you to specify which points, as long as they are flagged as out of control, to exclude from calculations with an easy tick box.
Of course if you are feeling really flash you can try the following.
Create the I-MR chart.
Brush the point that you dont want, right click the chart and select brush and then highlight the data point.
Rightclick again select make indicator variable, call it something like brushed, and let it update when the brushed set changes.
Then go back to the I-MR chart dialogue box, use Data options to exclude data where the brushed column =1.
Set the new I-MR chart to update automatically.
Then brush the first chart and watch the second update based on your selection in the first.
It works with stages as well.
You do have to use a second graph for this, as updating the chart removes the brushed points, which then cannot be brushed on the chart as they are not displayed.
Im not sure how useful doing that is, but its quite fun to play with
