Use a surface plot to help you visualize the response surface. Surface plots are useful for establishing desirable response values, mixture blends, and operating conditions.

A surface plot shows how a response variable relates to three components based on a model equation. Because a surface plot shows only three components at a time, while holding any other components and process variables at a constant level, the surface plots are only valid for fixed levels of the extra variables. If you change the holding levels, the response surface changes as well, sometimes drastically.

For the fondue data, previous investigation has shown that the flavor rating is highest when it is served at 90°. Therefore, Temperature has been fixed at 90.0 (high level). To maximize flavor, you would choose proportions for the components in the upper left corner of the plot. The blend that produces the highest flavor rating is at the vertex that is comprised of:

30% Emmenthaler (p = 0.3), 30% Gruyere (p = 0.3), and 40% Wine (p = 0.4)

The proportions of the components must be selected in such a manner that they sum to one.