x, y = new_pt

        exist = self.points_between(x, x + clear_ahead_secs)

        for pt in exist:

            self.remove_point(pt)

        self.insert_pt(new_pt)

        dispatcher.send("points changed", sender=self)

        # now simplify to the left

    def set_points(self, updates):

        for i, pt in updates:

            self.points[i] = pt

        #self.checkOverlap()

        dispatcher.send("points changed", sender=self)

    def checkOverlap(self):

        x = None

        for p in self.points:

            if p[0] <= x:

                raise ValueError("overlapping points")

            x = p[0]

    def pop_point(self, i):

        p = self.points.pop(i)