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The changing role of industry, the trend towards automation, the in­ creased cost of raw materials and labour rates all emphasize the need for improved quality of manufacture which will lead to better reliability, reduced maintenance costs and incidence of failure, as well as greater consumer confidence. Many countries, including Japan, are noted for their high quality of manufacture. This has helped them monopolize the world radio and television market and achieve great in-roads into the motor industry. If other economies are to compete effectively against such competition, then improvements in quality and performance of products are necessary. The need for control of quality embraces many fields from design, manufacture, function testing and inspection, through to an understand­ ing of sampling procedures and sampling theory, embracing both employee and management responsibilities to the maintenance of quality. The aim of this book is to give an understanding of industrial quality control. The techniques described have been selected so that they may be applied to industrial problems. It is hoped and expected that these methods will lead to improvements in quality and economics of manufac­ ture, thus leading to increased productivity and profitability. 9 1 The Need for Quality Control The major goals for quality control are manifold and include a need to determine the real functional tolerances required for engineering specifications and to provide a plan for control of the quality of the results of a process related to time. This is normally achieved by statistical or control chart methods