因为本程序使用 C# 的反射功能动态生成数学表达式并计算其值,所以重画时有点慢，如果你的计算机的速度不是非常快的， 就不要在窗口改变大小时强制重绘，而是通过点击发“刷新”按钮重绘。

-Because this program uses C# reflection function dynamically generated mathematical expressions and calculates its value, so when you re-painting a bit slow, if your computer' s speed is not very fast, do not change the size of the window to redraw force, but through Click issued " Refresh"　button to redraw.