Languages such as French, Spanish, and German required diacritics, special signs attached to or on top of the base letter: for example, a combination of the acute accent plus produced ; plus produced . In metal typesetting, , , and others were separate sorts. With mechanical typewriters, the number of whose characters (sorts) was constrained by the physical limits of the machine, the number of keys required was reduced by the use of dead keys. Diacritics such as (acute accent) would be assigned to a dead key, which did not move the platen forward, permitting another character to be imprinted at the same location; thus a single dead key such as the acute accent could be combined with ,, and to produce ,, and , reducing the number of sorts needed from 5 to 1. The typebars of "normal" characters struck a rod as they moved the metal character desired toward the ribbon and platen, and each rod depression moved the platen forward the width of one character. Dead keys had a typebar shaped so as not to strike the rod.