Summary: Multi-objective optimization takes care of different objectives with the objectives keeping their own units. The internal mechanical solution of a ratio system, producing dimensionless numbers, is preferred. The ratio system creates the opportunity to use a second approach: a reference point theory, which uses the ratios of the ratio system. This overall theory is called MOORA (multi-objective optimization by ratio analysis). The results are still more convincing if a full multiplicative form is added forming MULTIMOORA. The control by three different approaches forms a guaranty for a solution being as non-subjective as possible. MULTIMOORA, tested after robustness, showed positive results.