These are limited to one typographic line of symbols, which may include subscripts and superscripts. Commas in multi-component subscripts and superscripts are sometimes omitted; this is also potentially ambiguous notation. Usage of subscripts and superscripts is also an important convention. Descartes introduced the use of superscripts to denote exponents as well. Other digits, like superscripts, have numeric type Digit. Tensor products are denoted by superscripts, e.g., formula 4. The superscripts denote that these quantities are associated with the unperturbed system. Here the superscripts of the basis functionals are not exponents but are instead contravariant indices. Some word processors format ordinal indicators as superscripts by default (e.g. Microsoft Word). The charges of ions and subatomic particles are also denoted by superscripts. Exponents are usually formatted using superscripts, e.g. "x". In medieval German manuscripts, other digraphs were also commonly written using superscripts. Battle round advisors are listed first; additional advisors and their roles are denoted by superscripts. In this case, the components may be denoted by superscripts. Stations with the same name are differentiated, usually by company abbreviations as superscripts.