Hi @Anonymous
When the free form bar is set as keep straight, it is automatically matched to the first straight shape loaded into the project. For the standard template, shape 00, which has the segment length defined as B
If you edit the shape family and change that to A, for example, and reload into the project, you will see that the free form bar is reporting the segment as A
Since Revit 2022, you can also assign one of the other straight shapes in the project to a free form bar that is set as Keep Straight. For example a shape 99. If that one has a different parameter assignment (e.g. C) than the free form bar will report the length as such.
More about free form rebar shape matching here
https://help.autodesk.com/view/RVT/2022/ENU/?guid=GUID-054A2971-BA2D-46BF-A508-3D805F1C2666
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