Instructions How to Evaluate Control Chart


1. Observe the distribution, not the position of the control chart points.

It is to evaluate the distribution caused by the process.


2. When the points are in the restricted area, you don't have to worry about movement

Even when nothing was out of the ordinary, there was a random distribution in the data.


3. When the points are in the bounds, the process is essentially considered to be is under control.


4. When the points are out of bounds, the process is definitely out of control.

  When a point is on the control line the process is not under control. 


5. When the points are in the following cases, then the process should be controlled.

   a) 25 consecutive points within the limit range
   b) One (1) out of 35 consecutive points is out of range.
   c) Two (2) out of 100 consecutive points are out of range.


6. When 7 points in a row lie on one side of the quality, the process may be in an abnormal condition.

    The consecutive points on one side of the CL are ‘range (run)


7. The process is abnormal when ‘range’ appears as follows:

   a) A row of 10 points out of 11 in a row
    b) A sequence of 12 points out of 14 consecutive points
    c) A sequence of 14 points out of 17 consecutive points
    d) A sequence of 16 points out of 20 consecutive points


8. Process irregularities can occur when points lie in a trend going up or down.


9. When more than half of the points are out of bounds or most of the points are within the half between CL and U / L CL, the control chart is erroneous in the distribution group data or during stratification.


10. Check the pre-R-control chart in case of an X-R control chart.

X-R control chart.

Author: Phan Nguyen

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