Minitab estimates parameters by using an iterative algorithm to minimize the sum of squares of the residual error (SSE). You must supply the algorithm's starting values for each parameter. In addition, you can put constraints on the estimated parameter values in the fitted model.
For the single predictor expectation functions that Minitab supplies, view the function sketches in the catalog to help generate starting values. These sketches illustrate how the parameters are connected to portions of the response curve.
If you enter multiple starting values for at least one parameter, Minitab determines which starting value combination produces the smallest initial SSE and uses that combination to perform the nonlinear regression analysis. To view this combination, select Information for each iteration in the Results dialog box. Or, select Grid of starting values and SSE values in the Storage dialog box and examine the worksheet for the combination that produces the smallest initial SSE.