 Finite length coordinates for hyperbolic surfaces

For a fixed pants decomposition of a closed genus-$g$ hyperbolic surface, its $3g-3$ cuff lengths determine all its Y-pieces. Two suitably chosen transverse simple closed curves at each cuff, one obtained from the other by a Dehn twist, determine the corresponding twist: hyperbolic seam identities express their lengths through shifted hyperbolic cosines of that twist, removing the sign ambiguity of just one transversal. Thus finitely many marked lengths determine the Fenchel–Nielsen coordinates. The unmarked length spectrum lacks these labels, which is why this fact alone does not imply global spectral uniqueness.