Sets the maximum range for the currently selection calibration,
        determined from its range of values store on file

def maxRange(self):
        """Sets the maximum range for the currently selection calibration,
        determined from its range of values store on file
        """
        try:
            x, freqs = self.datafile.get_calibration(str(self.ui.calChoiceCmbbx.currentText()), self.calf)
            self.ui.frangeLowSpnbx.setValue(freqs[0])
            self.ui.frangeHighSpnbx.setValue(freqs[-1])
            print 'set freq range', freqs[0], freqs[-1], freqs[0], freqs[-1]
        except IOError:
            QtGui.QMessageBox.warning(self, "File Read Error", "Unable to read calibration file")
        except KeyError:
            QtGui.QMessageBox.warning(self, "File Data Error", "Unable to find data in file")