Double Sampling Plans for Inspection by Variables when the Process Standard Deviation is Unknown

Selects one of Hamaker′s procedures for deriving a “σ” method (i.e. known process standard deviation) double sampling plan and exploits some of its properties to develop a system of “ s ” method (i.e. unknown process standard deviation) double sampling plans by variables that match the system of single specification limit “ s ” method single sampling plans of the current edition of the international standard on sampling by variables. ISO 3951: 1989. The new system is presented in two forms, the second of which may also be used for combined double specification limits and multivariate acceptance sampling.