Product Summarization Sigma

Use this site parameter to change the multiplier used in Cpu, Cpl, Ppu, and Ppl calculations (these are used for Cpk and Ppk calculations). The default value is 3, which reflects the standard multiplier used in "6 sigma" calculations. For example, if the value is changed to 2, then rather than having 3σ as the divisor for the Cpu calculation, you would have a divisor of 2σ.

To change this site parameter:

  1. Log in to the Plant Applications Administrator.

You must have Administrator access to the Administrator security group to change site parameters.

  1. Open Global Configuration.

  2. Right-click Administer Site Parameters and choose Edit Site Parameters.

    The Site Parameters dialog box appears.

  3. Scroll down and double-click Product Summarization Sigma.

    The Edit Parameter dialog box appears.

  4. Enter a number from 1 to 4 in the Value box. The following formula shows how this number will be used:

Ppk = min( (USL - XBar) / (ProductSummarizationSigma * StDev), (xBar - LSL) / (ProductSummarizationSigma * StDev))

Cpk = min( (USL - XBar) / (ProductSummarizationSigma * Sigma), (xBar - LSL) / (ProductSummarizationSigma * Sigma))

  1. Click OK to save your changes and close the dialog box.

  2. Click to close the Site Parameters dialog box.

  3. Refresh the server.

For more information on Cp, Cpk, Pp, and Ppk calculations, see Variable Property Definitions.