For convertion between units, why not using the already built-in system of "Languages Translation" ? Hence, if people gives the value in Meter someone else could give it in Foot with the right precision and there will just be a link of "Translation" between those two Same apply for Units being given in SI ("kg⋅m2⋅s−3⋅A−2") and a Translation to "Ohm" My two cents Mohamed -- Innovimax SARL Consulting, Training & XML Development 9, impasse des Orteaux 75020 Paris Tel : +33 9 52 475787 Fax : +33 1 4356 1746 http://www.innovimax.fr RCS Paris 488.018.631 SARL au capital de 10.000 €