code: def dx(self):
          
          try:
              return self._dx
          except AttributeError:
              try:
                  self._xindex
              except AttributeError:
                  self._dx = Quantity(1, self.xunit)
              else:
                  if not self.xindex.regular:
                      raise AttributeError("This series has an irregular x-axis "
                                           "index, so 'dx' is not well defined")
                  self._dx = self.xindex[1] - self.xindex[0]
              return self._dx
docs: X-axis sample separation
  
          :type: `~astropy.units.Quantity` scalar