Recently spotted some code in an official SDK sample:
arr.Append(m_revit.Create.NewArc(pnt2, 1.0d, 0.0d, 180.0d, Autodesk.Revit.DB.XYZ.BasisX, Autodesk.Revit.DB.XYZ.BasisY));
It seems the intent was to create a half circle arc, on the XY plane, as part of a profile which was used to create a sweep next. However, it does not look right at all because of the simple fact that only radian angle values are accepted in the Create.NewArc method. By the way, the d suffix indicates the value is a double instead of a 'DEGREE'.
The odder part is that the sample still runs in Revit! So compiling and running does not really indicate everything is fine. Some tricky issues may hide deep.