Data - Surface Plot
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You must fit a regression model with at least two continuous predictors before you can generate a surface plot. Minitab looks in the worksheet for the stored model to obtain the information necessary to generate the plot.

Surface plots are model dependent. Minitab estimates the response surface based on the most recently fit model for the specified response. For this reason, it is important that the last model you fit is the best model to describe the relationship between the response and the predictors. The surface plot is accurate only if the model represents the true relationship.