说明：  此种方法比较原始，适合于即时数据，原理是先画上一帧，接着保留原始图像，追加下一幀图像，此种方式比较繁琐，涉及画图细节，并且没有完整并连续的Line对象数据。此种方法需要注意的地方是，若想生成连续的线图，则每次plot至少两个点，原理大家都应该理解，两点一线嘛！如果想每次一个点增量式的画图，则线型选择’.’。
(This method is relatively primitive and suitable for real-time data. The principle is to draw a frame first, then retain the original image and add the next frame of image. This method is cumbersome and involves drawing details, and there is no complete and continuous Line object data.The important thing about this method is that if you want to generate a continuous plot, you need at least two points per plot. The principle should be understood.If you want to draw incrementally one point at a time, select '. '.)