Geometric tolerance

[john s]

I am new in CMM, and have IMS impact, VDMIS 6.0, I've simple U Shape part to findout the symmetry of two outer lines with two inner lines (model attached), but unfortunately I failed. It gives wrong values as compare with another CMM report.
Then I made a model on pro-e and intentionally give 0.02mm error in mid lines of both side so that I could see the behavior in OFF LINE mode.
Process of working: After alignment I took two external lines left and right and make middle of it for datum and then took two internal left and right lines and take points as well because the symmetry box didn’t accept the lines as a reference I thinks there were limitations to accept reference features.
After that I opened the symmetry option and give middle line as a datum and give two left and right points as a reference, but it gives 0.02mm value. I think it has to give 0.04 value because I give 0.02mm difference in mid lines in model and if I am not wrong the symmetry value must be twice of the difference (distance between the middle of both external and internal lines),please guide or suggest me where i am wrong?

Thanks in advance
John

[IVDMIS]

The following is from "ASME Y14.5M-1994".

"Symmetry is that condition where the median points of all opposed or correspondingly-located elements of two or more feature surfaces are congruent with the axis or center plane of a datum feature."

So I think it should be 0.04...

Please post if the above is not correct...