code: def calcdelay(self, ant1, ant2, skyfreq, pol):
          
  
          select = self.select[n.where( (self.skyfreq[self.select] == skyfreq) & (self.polarization[self.select] == pol) )[0]]
  
          ind1 = n.where(ant1 == self.antnum[select])
          ind2 = n.where(ant2 == self.antnum[select])
          d1 = self.delay[select][ind1]
          d2 = self.delay[select][ind2]
          if len(d1-d2) > 0:
              return d1-d2
          else:
              return n.array([0])
docs: Calculates the relative delay (d1-d2) for a pair of antennas in ns.