text: The thermodynamic observables we have investigated 
  
  entering the deﬁnition of κ in Eq. (4)), we remind that 
  such quantity has generally to be managed with particu- 
  lar care, as discussed in details in Refs.14,15, where it was 
  shown that the presence of block structures prevents us 
  to unambiguously relate the evolution of S(~q) with the 
  onset of helical order. However, for the speciﬁc case of 
  the model under investigation such integrated quantity 
  can still be considered a fairly signiﬁcant order parame- 
  ter, as no block structures emerge from the simulations 
  (see below). 
  
  include the FM order parameter for each plane l: 
  
  1 
  n 
  M =  ml .  (3) 
  Xl=1 
  
  In order to get a clear picture of the critical region and 
  to give an accurate estimate of the critical temperature, 
  we look also at the following quantities 
  
  Turning to the helical order, which is the relevant 
  quantity for the Z2 × SO(2) symmetry, we can explore 
  it along two diﬀerent directions. The ﬁrst one is by the 
  introduction of the chirality order parameter1,2 
  (6) 
  
  (7) 
  
  (8) 
  
  u4(o) = 1 −  (9) 