利用TpaintBox的Canvas绘从串口收取的实时心电波形及备景程序，绘制网格程序已封成一个Function，可以直接用到别的地方，如绘窗口背景网格只要改几个参数就可以了

Draw compass It uses a TPaintbox, Compass , to repaint the compass when needed. Compass is completely redrawn for each call so its owner (Panel1) has its Doublebuffered property set True to prevent flashing when the space is cleared before redrawin