text: from matplotlib.dates import date2num
  import numpy as np
  
  def polyfit(dates, levels, p):
      """Returns a pth degree polynomial fit along with the origin offset for given dates and levels"""
  
      t0 = date2num(dates[-1])
      t = [date2num(i) - t0 for i in dates]
  
      p_coeff = np.polyfit(t, levels, p)
  
      return np.poly1d(p_coeff), t0
  
  def relative_levels(levels, station):
      """Converts a list of level data to a list of relative level data for a given station"""
  
      if not station.typical_range_consistent():
          return None
      else:
          min, max = station.typical_range
          return [(i - min)/(max - min) for i in levels]