...u (defect density) charts. All are well-established quality management tools, but modern computer technology offers alternatives.

Traditional attribute charts have a drawback that becomes more serious as quality levels improve. Calculation of their control limits relies on the normal approximation to the binomial and Poisson distributions. This requires an expected count of four to six events--rework, scrap or defect--per sample: which is not good quality by modern standards.

Spreadsheets allow quality practitioners to not only use the actual binomial or Poisson distribution but also to track multiple problem sources. A multiple attribute control chart is the simplest of the traditional problem-solving tools: a check sheet or tally sheet. Additional spread sheet programming provides a warning when the process is out of control. William Levinson and Frank Tumbelty's book, SPC Essentials and Productivity Improvement: A Manufacturing Approach, lists the following advantages:

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NOTE: All illustrations and photos have been removed from this article.



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