code: def ent_tank_a(self):
          
          # first guess planview area
          a_new = 1 * u.m**2
          a_ratio = 2  # set to >1+tolerance to start while loop
          tolerance = 0.01
          a_floc_pv = (
              self.floc.vol /
              (self.floc.downstream_H + (self.floc.HL / 2))
          )
          while a_ratio > (1 + tolerance):
              a_et_pv = a_new
              a_etf_pv = a_et_pv + a_floc_pv
              w_tot = a_etf_pv / self.floc.max_L
              w_chan = w_tot / self.floc.channel_n
  
              a_new = self.floc.max_L * w_chan
              a_ratio = a_new / a_et_pv
          return a_new
docs: Calculate the planview area of the entrance tank, given the volume of
          the flocculator.
  
          :returns: The planview area of the entrance tank.
          :rtype: float * u.m ** 2