The correct matches are based on formal Function Analysis classification. SAVE defines a function as what a project, product, or process must do, independent of what it is or how it is accomplished, and it should be stated in active verb/measurable noun form. A basic function is the specific purpose for which the product exists and answers “What must it do?” For prescription eyeglasses, that purpose is Correct vision . SAVE’s function-analysis examples for spectacles also classify Correct Vision as the basic function.

A higher order function represents the broader need or outcome that causes the basic function to exist. Correcting vision exists to Enhance vision , so that is the best higher-order match. A lower order function is outside the study scope and represents a required input. For prescription eyeglasses, the prescription must be determined first; therefore Assess vision is the best lower-order function. A secondary function supports the basic function and results from the selected design approach. In eyeglasses, the frames, bridge, arms, and related hardware support the basic function by Positioning lenses correctly in front of the eyes. “Fit face” is also a supporting idea, but it is less direct than “Position lenses” for this one-slot secondary classification.

References/topics: Function Analysis Phase; Basic Function; Higher Order Function; Lower Order Function; Secondary Function; FAST Logic.