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5. Process Improvement
5.5. Advanced topics
5.5.9. An EDA approach to experimental design DOE contour plot

How to Interpret: Steepest Ascent/Descent

Start at optimum corner point From the optimum corner point, based on the nature of the contour surface at that corner, step out in the direction of steepest ascent (if maximizing) or steepest descent (if minimizing).
Defective springs example Since our goal for the defective springs problem is to maximize the response, we seek the path of steepest ascent. Our starting point is the best corner (the upper right corner (+, +)), which has an average response value of 88.5. The contour lines for this plot have increments of 5 units. As we move from left to right across the contour plot, the contour lines go from low to high response values. In the plot, we have drawn the maximum contour level, 105, as a thick line. For easier identification, we have also drawn the contour level of 90 as thick line. This contour level of 90 is immediately to the right of the best corner
Conclusions on steepest ascent for defective springs example The nature of the contour curves in the vicinity of (+, +) suggests a path of steepest ascent
  1. in the "northeast" direction
  2. about 30 degrees above the horizontal.
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