def _identify(self, dataframe):
        """Return bool series which is True for indexes that 'pass' the gate"""
        idx = ((dataframe[self.channels[0]] <= self.vert[1]) &
               (dataframe[self.channels[0]] >= self.vert[0]))

        if self.region == 'out':
            idx = ~idx

        return idx
Return bool series which is True for indexes that 'pass' the gate