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Defective Units

A defective unit is a unit that has one for more defects.  Inspections for defective units generally count the number of defective units.  An exception is the variable sampling plans for defective units, which estimate the number of defective units by taking physical measurements and applying the normal distribution.  An alternative to counting the number of defective units is to count the number of defects.

The types and sources of sampling plans for defective units are:
  • Single
  • Double
  • Multiple
  • ANSI Z1.4
  • Variables Single
  • ANSI Z1.9
     
    Many prefer to use the term nonconforming units to clarify that a unit that fails to meet the requirements does not necessarily imply that it is unfit for use.  For example, a requirement may have been set for a particular dimension.  Passing the requirement ensures proper assembly of the parts.  But failure to meet requirements does not imply the parts will not assemble properly.  It only means that proper assembly cannot be guaranteed.