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Historical Perspective

Quality Control has been with us for a long time. How long? It is safe to say that when manufacturing began and competition accompanied manufacturing, consumers would compare and choose the most attractive product (barring a monopoly of course). If manufacturer A discovered that manufacturer B's profits soared, the former tried to improve his/her offerings, probably by improving the quality of the output, and/or lowering the price. Improvement of quality did not necessarily stop with the product - but also included the process used for making the product.

Statistical Process Control (SPC)

Typical process control techniques:

There are many ways to implement process control. Key monitoring and investigating tools include:

  • Histograms
  • Check Sheets
  • Pareto Charts
  • Cause and Effect Diagrams
  • Defect Concentration Diagrams
  • Scatter Diagrams
  • Control Charts

Statistical Quality Control (SQC)

Tools of statistical quality control

Several techniques can be used to investigate the product for defects or defective pieces after all processing is complete. Typical tools of SQC are:

  • Lot Acceptance sampling plans
  • Skip lot sampling plans
  • Military (MIL) Standard sampling plans