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