\setlength{\gnat}{length}
The \setlength command is used to set the value of a length command. The length argument can be expressed in any terms of length LaTeX understands, i.e., inches (in), millimeters (mm), points (pt), etc.
\setlength{\gnat}{delka}
Prikaz \setlength se pouziva k nastaveni hodnoty delkoveho prikazu. Hodnota delky muze byt vyjadrena v libovonych delkovych jednotkych, ktere LaTeX podporuje: palce (in), milimetry (mm), body (pt), a dalsi.