Fenchel–Nielsen coordinates
= Fenchel–Nielsen coordinates
{c}
{title2=$(\ell_1,\ldots,\ell_{3g-3},\tau_1,\ldots,\tau_{3g-3})$}
{wiki}
For a fixed <pants decomposition>, the positive cuff lengths and real twist parameters give coordinates on <Teichmüller space>. With twists measured in length units, a full <Dehn twist> changes $\tau_i$ by $\ell_i$; with angle units it changes the twist by $2\pi$.