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	Application Setup

Application Setup Calculations Page

The Calculations page of RGA's Application Setup allows you to set the numerical precision used in the calculated results and plots.

• Precision to be Displayed on Calculations

• • Use Displayed math precision to set the number of decimal places shown in results and plots. Please note that the tolerance on the precision is limited by Windows to 15 digits.

  • Use Scientific notation tolerance (10^?) to set the point at which the software will switch to scientific notation. For example, if the scientific notation tolerance is set to 5, then any number that is larger than 10⁵ will be displayed using scientific notation.

• The Failure Discounting area applies only to the Discrete Sequential with Mode data type. Specify the confidence level that will be used to define the fractional decrease in failure value. (See Failure Discounting.)

• The Crow/Power Law Models area applies only to calculations using the Crow-AMSAA (NHPP), power law, Crow Extended or Crow Extended - Continuous Evaluation models. Select whether to display the value of the power law parameter, Lambda, or the Weibull parameter, Eta, in the analysis results.

• The Duane Model area applies only to calculations using the Duane model. Select whether to display the value of the A parameter (cumulative failure intensity) or the b parameter (cumulative MTBF) in the analysis results.

• The Crow Extended Model area applies only to calculations using the Crow Extended or Crow Extended - Continuous Evaluation models.

• • Select Show Crow-AMSAA beta for beta = 1 hypothesis to display the value of the beta parameter for the Crow-AMSAA (NHPP) model in addition to the hypothetical value of beta calculated for the Crow Extended or Crow Extended - Continuous Evaluation models, as shown in the following example.

• • Select Allow EF values for BD modes with implemented fixes to add a second tab in the Effective Factors window when you are using the Crow Extended - Continuous Evaluation model. This allows you to record the effectiveness factors for BD modes that were fixed during testing. Note that this functionality is for your information only; it is not used in calculations.

• The Instantaneous MTBF/FI at the End of Development Testing area allows you to specify whether the instantaneous MTBF and failure intensity at the end of the test will be shown in the analysis results with the term “demonstrated” (i.e., DMTBF/DFI) or “achieved” (i.e., AMTBF/AFI).

• User Warnings

• • Select Beta = 1 hypothesis is invalid if you want RGA to display a message when the beta = 1 hypothesis fails. This warning applies only to the Crow Extended or Crow Extended - Continuous Evaluation models.

  • Select Model parameters out of range if you want RGA to display a message when the value of the k parameter (logistic model) or Alpha parameter (Lloyd-Lipow model) is less than or equal to zero. Negative values indicate that the analysis results may not be valid.

  • Select Effectiveness factors of zero if you want RGA to display a message when one or more effectiveness factors equal to zero. This warning applies only to the Crow Extended or Crow Extended - Continuous Evaluation models.

• Other Options

• • Select Use percents (not decimals) for reliability to enter and display reliability values as percentages (e.g., 90) rather than decimals (e.g. 0.90). This applies to the Reliability data type only.

  • Select Data input is cumulative to configure the data sheet for cumulative failure times, by default, instead of non-cumulative failure times. (See Cumulative vs. Non-Cumulative Data.)

  • Select Calculate unbiased beta to remove the bias of the MLE estimate of the beta parameter, when applicable. An unbiased estimate will be labeled in the results as "Beta (UnB)" instead of "Beta." For more information, the "Unbiasing Beta for the Crow-AMSAA (NHPP) Model" article at: http://www.weibull.com/hotwire/issue141/hottopics141.htm demonstrates how the bias is corrected for Crow-AMSAA (NHPP). This is also applicable to the Crow Extended, Crow Extended  - Continuous Evaluation and power law models.