code: def calc_qref_v1(self):
      
      new = self.sequences.states.fastaccess_new
      old = self.sequences.states.fastaccess_old
      flu = self.sequences.fluxes.fastaccess
      flu.qref = (new.qz+old.qz+old.qa)/3.
docs: Determine the reference discharge within the given space-time interval.
  
      Required state sequences:
        |QZ|
        |QA|
  
      Calculated flux sequence:
        |QRef|
  
      Basic equation:
        :math:`QRef = \\frac{QZ_{new}+QZ_{old}+QA_{old}}{3}`
  
      Example:
  
          >>> from hydpy.models.lstream import *
          >>> parameterstep()
          >>> states.qz.new = 3.0
          >>> states.qz.old = 2.0
          >>> states.qa.old = 1.0
          >>> model.calc_qref_v1()
          >>> fluxes.qref
          qref(2.0)