code: def _normalise_series(X, mean):
      std = np.std(X)
      if std > 0:
          return (X - mean) / std
      return X
  
imports: import math
  import numpy
  from sktime.utils.numba.njit import njit
label_desc: Use image node_id 14 for calling a global function with example usage: _normalise_series(X, mean) and returns: X, unknown