Axiomatic design theory, in its decoupled form, provides guidance for the design process to result in functionally reliable engineering systems that satisfy the requirements of some safety specification. The decoupled form can conveniently be obtained whenever the design problem is susceptible to dimensional analysis. However, both the ensuing dimensionless groups and the environment in which the system operates are intrinsically fuzzy. A tool for performing arithmetic and logical operations in the fuzzy environment is the t-norm. Experience indicates that only one t-norm, the min-operator originally proposed by L.A. Zadeh and known as Zadeh's Extension Principle, ZEP, is congruent with results of engineering experiments. This extension principle is reviewed in the paper, and its applicability demonstrated on a real-world example.