def METHOD_NAME(self):
    # Returns the questionnaire ID or "None" if it cannot be retrieved
    # In this function assume that the rotation is correct already.
    paper_width = self.obj.sheet.survey.defs.paper_width
    paper_height = self.obj.sheet.survey.defs.paper_height
    # Search for the barcode on the bottom left of the page
    code = \
        read_barcode(self.obj.surface.surface, self.obj.matrix.mm_to_px(),
                     0,
                     paper_height - self.obj.sheet.survey.defs.corner_mark_bottom - defs.code128_vpad - defs.code128_height - 5,
                     paper_width / 2,
                     self.obj.sheet.survey.defs.corner_mark_bottom + defs.code128_vpad + defs.code128_height + 5)
    # Simply return the code, it may be alphanumeric, we don't care here
    # XXX: Is that assumption sane?
    return code