So the arrow is poiting the surface. There's contact when you're using the preposition " on" .

所以箭头指向表面。 当你使用介词“on” 时有联系。

So there's a method of contact there. So when we show that graphically Here's how we can draw that. Draw a surface, and draw the arrow poiting onto the surface.

所以那里有一种联系方式。 因此，当我们以图形方式显示时，这就是我们如何绘制它。 绘制一个曲面， 并绘制指向该曲面的箭头。