2.5.2 Rejection of formal units
A formal unit may be rejected, or its use abandoned, if it proves to (a) be equivalent to a previously formally defined unit, (b) be defined in the wrong category, (c) not have any application, and (d) be used in many different ways. The proper name of a formal or informal unit that has been rejected may be used for a subsequently newly erected unit if a long period has passed after the name was used in its original meaning.