I'm trying to get the total length (at 3 decimal point) from start station to end station of a component (say road pavement). So I had the following expression:

System.Math.Round(this.GetElement().GetDisplayValue("MeshSurfaceEntity_EndStation")-this.GetElement().GetDisplayValue("MeshSurfaceEntity_StartStation"),3)

However it failed to give me any value.

Would appreciate any Samaritan out there to see what's wrong with the expression and advise on a solution.

Thank you in advance.