def start(self):
        self.instructions()
        # start ruler drawing operation
        p_canvas = self.fitsimage.get_canvas()
        try:
            obj = p_canvas.getObjectByTag(self.layertag)

        except __HOLE__:
            # Add ruler layer
            p_canvas.add(self.canvas, tag=self.layertag)

        self.resume()
dataset/ETHPy150Open ejeschke/ginga/ginga/misc/plugins/Compose.py/Compose.start