2. Listen to the voice of the process

In order to spot abnormal variations that herald new trends or particular events, the theory of variations requires us to trace the natural limits of the process that produces our measurement or indicator.

We complete the chronological graph of observations with two limits that frame the average: the natural upper limit of the process (LSNP) and the natural lower limit of the process (LINP).

Variation theory tells us that :

• any value within these limits is a normal value for the process or system observed by our indicator or measurement. Variations between different measurements can be considered as noise. There is no point in looking for specific causes for these variations, which are the result of the combination of multiple variations present in the process or system;

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