Occasionally you may want to create a segment of fixed length — for instance, a segment that is exactly 0.8 cm in length. While you could create a segment with the Segment tool, measure its length, and drag one endpoint until its length was 0.8 cm, this segment would not be constructed to be fixed at 0.8 cm long. That is, dragging an endpoint again would change it from its current length to some other length.
If the distance units are not cm, use Edit | Preferences | Units to set them to cm before doing this step.
2.Use the Point tool to construct a point; this will be the first endpoint of the segment.
3.Select the point and the parameter. Choose Construct | Circle by Center+Point to construct a circle whose radius is determined by the parameter.
4.Use the Segment tool to construct a radius of the circle. This is the segment of fixed length.
5.Hide the parameter and the circle.
6.Drag either endpoint of the segment to see how it behaves.