For a printed medium (such as paper), a typographic approximation is a replacement (approximation) of some element of the writing system (usually, a glyph) with some else glyph(s), such as a nearly homographic character, digraph or character string. An approximation is different from a typographical error in that an approximation tries to preserve visual appearance of a glyph. There are approximation for non-printed visual presentation such as displays.