docs: def compute_refresh_time(self):
          """ Compute the refresh period for the given expiration delay """
          if self.z == 0:
              self.z = 1E-10
          s = float(self.expiration) * (1.0/(self.nbr_bits)) * (1.0/(self.counter_init - 1 + (1.0/(self.z * (self.nbr_slices + 1)))))
          return s