text: where S(~q), with ~q = (0, 0, qz), is the structure factor24 
  (i.e. the Fourier transform of the spin correlation func- 
  tion) along the z-direction of the ﬁlm, while the normal- 
  ization factor K is the structure factor integral at T = 0. 
  Although the use of the last observable can be seen as a 
  suitable and elegant way to overcome the intrinsic diﬃ- 
  culties met in deﬁning a correct helical order parameter, 
  free of any undue external bias (as the wave-vector Qz 