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Part Three
Planning and control
Figure S17.10 In addition to points falling outside the control limits, other unlikely sequences of points should be
investigated
Interpreting control charts
Plots on a control chart which fall outside control limits are an obvious reason for believing
that the process might be out of control, and therefore for investigating the process. This is
not the only clue which could be revealed by a control chart, however. Figure S17.10 shows
some other patterns which could be interpreted as behaviour sufficiently unusual to warrant
investigation.
Process control, learning and knowledge
In recent years the role of process control and SPC in particular, has changed. Increasingly,
it is seen not just as a convenient method of keeping processes in control, but also as an activity
which is fundamental to the acquisition of competitive advantage. This is a remarkable shift
in the status of SPC. Traditionally it was seen as one of the most operational, immediate
and ‘hands-on’ operations management techniques. Yet it is now being connected with an
operation’s strategic capabilities. This is how the logic of the argument goes:
1 SPC is based on the idea that process variability indicates whether a process is in control
or not.