Delft Design Guide | Part 2 | Decision and Selection | Datum Method –
How to
Datum Method
an existing product a similar product
list of criterias and alternatives
Tips and Concerns • Sometimes the designer will not only totalise the
arrange all criteria and alternatives in a matrix
choose a ‘datum’
of the design process. However one may have some ideas about the relative difference in cost price. E.g.
score in ∑+, ∑ S and ∑ –, but also adds up the
one concept seems to be more expensive than the
totals. Like each ‘+’ for one particular concept is
other one, because of a larger number of parts or a
compensated by each ‘-’ given to the same concept.
more complex construction. In choosing the (more
A concept with two ‘+’, one ‘S’ and two ‘-’ will have
general reformulated criteria) it seems logical not to
an end score of zero (0). Although it is a way to have
have more than eight to ten criteria.
some outcome, one must realise that this will fade away the results and doesn’t help to discuss the
References and Further Reading
concepts or criteria. Another concept might score
Pugh, S. (1981) ‘Concept selection: a method that works’ In:
zero (0) also, thus leading to the assumption that
Hubka, V. (ed.) Review of Design Methodology. Proceedings
both concepts are equal, while the second concept
International Conference on Engineering Design, March 1981,
initially scored one ‘+’, three ‘S’ and one ‘-’. It all
Rome. Zürich: Heurista, 1981, pp.497 – 506.
depends on the weight of each criterion and the possibility to change a ‘-’ into ‘S’ or ‘+’ by redesign. The method is therefore not to be seen as a sort of
Roozenburg, N.F.M. and Eekels,J. (1995) Product Design: Fundamentals and Methods, Utrecht: Lemma.
mathematically justified process, but as an aid to the
Roozenburg, N. and Eekels, J. (1998, 2nd ed.) Product
decision making.
Ontwerpen: Structuur en Methoden, Utrecht: Lemma.
• Another aspect is the selection of criteria. Usually there are a lot of criteria to which the concepts do not comply to, yet. A criterion stating that the product should cost no more than 15 Euro’s, or weigh max 800 grams, cannot be judged in the early stages
+ = better than datum – = worse than datum
+ + ++ - + ++ - - s s
s = similar/same
compare properties of alternatives with those of datum
compare scores
2.3