Choose the distribution that the T chart is based on and enter the historical value for parameters that Minitab uses to calculate the center line and control limits. If you do not enter values, Minitab estimates the shape and scale from the data.
- Base the chart on the following distribution
- Select Weibull or Exponential. The exponential distribution is equivalent to a Weibull distribution with a shape parameter 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 parameter of the Weibull distribution. The 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.
- Enter a historical value for the scale parameter. The 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.