See the point in the middle, at the origin, is a saddle point. If you look at the tangent plane to this graph, you will see that it is actually horizontal at the origin.

我们来看中间的那个点，在原点上，那就是一个鞍点，在这点做一个切平面,你可以看到这个切平面,是在原点上水平的。

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X coordinates: The X coordinate is a point's horizontal distance from the origin.

X 坐标：X 坐标是某一个点距离原点的水平距离。

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Use to add a single horizontal ordinate dimension. Attach one endpoint to ordinate origin and one to the feature.

用于添加一个水平坐标尺寸。将一个端点连接到坐标原点，一个端点连接到部件。

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