def set_viewlimits(self, panel='top'):
        """update xy limits of a plot, as used with .update_line() """
        this_panel = self.get_panel(panel)

        xmin, xmax, ymin, ymax = this_panel.conf.set_viewlimits()[0]
        # print("Set ViewLimits ", xmin, xmax, ymin, ymax)
        # make top/bottom panel follow xlimits
        if this_panel == self.panel:
            other = self.panel_bot
            for _ax in other.fig.get_axes():
                _ax.set_xlim((xmin, xmax), emit=True)
            other.draw()
update xy limits of a plot, as used with .update_line()