Supersonic flows are similar if the mach number is constant. Convective flows are similar if the Nusselt number is constant. Buckingham pi analysis is a common method of determining dimensionless parameters. The decision matrix is a quantitative approach to engineering decision making. Weights are then defined for the criteria which represent the relative importance of each criterion.
Weights are usually numbers between zero and one.
Each concept is then evaluated against each criterion and given a numerical score. All scores MUST lie within the same range of numbers. This evaluation of the concepts is a quantitative benchmarking process. Finally, the weighted sum of each concept's scores is computed. The concept with the highest weighted sum is the most desirable.