def METHOD_NAME(self):
    if self.current_index <= self.numpoints / 3:
        self.increment = 2
    elif self.current_index == self.numpoints:
        self.increment = -2
    self.current_index += self.increment
    if self.current_index > self.numpoints:
        self.current_index = self.numpoints
    self.plot.index.set_data(self.x_values[: self.current_index])
    self.plot.value.set_data(self.y_values[: self.current_index])
    self.plot.request_redraw()