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The steps of an arc definition with its start, end point and tangent:

1. Define the start point of the arc by giving coordinates or   mouse-clicking.
2. Define the end point of the arc by giving coordinates or   mouse-clicking.
3. Set the tangent side with   mouse-clicking. Define the tangent direction from the start point with a third point (e.g. a point on a tangentially connected line) by giving coordinates or   mouse-clicking.

Figure: Some examples for defining structural objects with Arc by 3 points

Figure: Although same definition points are defined, the tangent side is different