Pranay Kumar -
SPC developed in 1920s in Bell Laboratories by Sir Walter Shewart is the best known amalgamation of statistics and engineering. Control Charts are most widely used method of understanding process behaviour with or without the customer specification.
They help distinguish between specific, identifiable causes or conditions that are directly responsible for process shifts (special or assignable-cause variation) and the collection of conditions inherent in any process that, taken together, result in cyclic variation of output around the process mean common-cause or chance variation.) A control chart consists of a center line and statistically determined upper and lower control limit lines against which time-sequenced data points are plotted.