ABSTRACT
The standard method of control by time plots from samples is the Shewhartian charts which are based on sampling, probability, and statistics. These charts are described in detail in the next chapter.
The heart of control is to obtain stability in a characteristic by keeping it within tolerated limits or bounds about a specified level. Shewhartian charts obtain and maintain stability by a process of detection. Detection leads to the elimination of assignable causes - factors that shift the levels and bounds beyond what are specified. All charts, however, start with a time plot of a key characteristic estimated from a sample and plotted in time sequence from successive samples.
