Control limits, also known as natural process limits, are horizontal lines drawn on a statistical process control chart, usually at a distance of ±3 standard deviations of the plotted statistic from the statistic's mean.
Control limits should not be confused with tolerance limits or specifications, which are completely independent of the distribution of the plotted sample statistic. Control limits describe what a process is capable of producing (sometimes referred to as the “voice of the process”), while tolerances and specifications describe how the product should perform to meet the customer's expectations (referred to as the “voice of the customer”).
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Famous quotes containing the words control and/or limits:
“The awareness that health is dependent upon habits that we control makes us the first generation in history that to a large extent determines its own destiny.”
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“The great disadvantage, and advantage, of the small urban bourgeois is his limited outlook. He sees the world as a middle- class world, and everything outside these limits is either laughable or slightly wicked.”
—George Orwell (1903–1950)