The unsupported length depends on fill weight
X axis: unsupported length in m FLB/FLG
Y axis: fill weight in kg/m
Lower scale: travel S in m
FLB = unsupported with permissible sag
FLG = unsupported with straight upper run
Reference example A:
fill weight = 0.75 [kg/m]
unsupported length FLB = 1.0 m
travel = 2.0 m