Remove Point from Control Chart Calculations

Ghost a Point - remove from calcuations but not from the chart.

While it is not usually recommended, many customers have asked for the ability to leave a point on a control chart BUT remove the point from the control limit calculations. Using the chart menu, QI Macros now give you this capability.

To remove a point from the calculations but leave it on a chart:

  1. Click on the point to be removed:
    select point on a control chart

    Tip: The first time you click on a point, Excel will select the whole line. Click on the point a second time to select just the point. If you have done this correctly, Excel will highlight your point.

  2. Next, select the QI Macros Chart menu and choose, "Ghost Point" from the "Process Changes" drop-down:

  3. The point marker will change to designate that the point has been "ghosted":
  4. point marker changes for a ghosted point on a control chart

  5. Next, re-run stability analysis with the new control limits (visual representation of your ghosted point(s) will be removed from the data point(s) when stability analysis is run).
  6. If you want to check the control limit calculations, go to the data sheet where the formulas are created and click on one of the average cells. Look in the formula box to view the formula. You will notice that the row that the ghosted point is in has been removed from the calculations. In the example below, the point in row 19 has been removed:
  7. control chart calculations with ghosted point removed

  8. You may also want to add text to the point to further highlight that it has been removed from the calculations.

NOTE: If you wish to remove any ghosted points from your data set, select the chart and choose "Recalculate UCL/LSL" from the "Process Changes" drop-down. Once you have done so, click on your chart and select "Analyze Stability" - this will reset all limit calculations and unghost your point(s).


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