When using 'Instance Geometry - Mirror' (in NX 8.5), or 'Mirror Geometry' (in NX 9 and later), to create the opposite hand of a model, the weight value of the part will be incorrect. This is because the 'Model' Reference Set will contain the body of both the original and mirrored copy of the model, resulting in the part having twice the expected volume.
Solution
To ensure that the weight calculation for the part is correct, the original body should be removed from the 'Model' Reference Set, after the mirror operation has been performed. To do this use the command 'Format - Reference Sets', select 'Model' from the list of Reference Sets, and then hold down the 'Shift' key and select the body that was the input to the Mirror command.
Notes and References
Hardware/Software Configuration
Platform: INTL64
OS: window
OS Version: 764SP1
Product: NX
Application: DESIGN
Version: V8.5
Function: FEATURE_MODEL
Ref: 001-1977298