The use and abuse of the terms percent, parts per million and parts in 10(n)

We discuss two different ways in which terms such as percent (%) and parts per million (ppm) are used, both in the scientific literature and in everyd ay language. We give examples of the way in which these terms may be used w ithout ambiguity, and we also describe common misuse of the terms. We sugge st the adoption of the special name uno (symbol U) for the unit one, for us e with the International System of Units (SI) prefixes in place of terms su ch as percent and parts per million in the technical literature.