y = [ -1.36633487e+01,  1.13808691e+01,  -8.92628692e+00,  6.53052299e+00, \
  -5.26897045e+00,  5.75429171e+00,  -1.75746114e+00,  1.39318500e-01, \
  -1.04863080e+00,   1.46985567e-02,   -1.04432984e+00,   1.14839620e+00, \
  -1.45837648e+00,  2.62571957e+00,  -4.64780802e+00,  4.02915206e+00, \
  -6.94357281e+00,  1.02403468e+01,  -1.30960565e+01,  1.55355021e+01]
x = [ 50.0,          51.05263158,  52.10526316,  53.15789474,  54.21052632, \
  55.26315789,  56.31578947,  57.36842105,  58.42105263,  59.47368421, \
  60.52631579,  61.57894737,  62.63157895,  63.68421053,  64.73684211, \
  65.78947368,  66.84210526,  67.89473684,  68.94736842,  70.        ]

r = hfitoff(y, x)
#plot([y,r[5]], ["data", "fit"], [x, r[4]])
plot([y,r[5]], [x, r[4]])