Options - Parameters
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Stat > Control Charts > Rare Event Charts > T > T Chart Options  > Parameters

Choose to base the calculations for  your T chart on a Weibull or an exponential distribution.

You can also enter historical parameters for either distribution. For example, if you have known process parameters or estimates that were obtained from past data, enter the values. If you do not specify values, then Minitab estimates the parameters from the data.

If you want to use historical parameters for the Weibull distribution, you must specify values for both shape and scale.

Dialog box items

Base the chart on the following distribution: Choose to base the calculations for your T chart on a Weibull or an exponential distribution. The exponential distribution is equivalent to a Weibull distribution with a shape of 1. If you choose the exponential distribution, then Minitab sets the shape parameter for the distribution to 1.

Shape: (Weibull distribution only) Enter a historical value for the shape of the Weibull distribution. Shape must be greater than 0. Historical values between 0.5 and 2 are the most practical. If you enter one value, then all stages use that value. Otherwise, enter a value for each stage.

Scale: Enter a historical value for scale. Scale must be greater than 0. Your historical scale value should be approximately equal to the mean of the data. If you enter one value, all stages use that value. Otherwise, enter a value for each stage.