When attaching a reference model that uses another geographic coordinate system than the model to which it is being attached, MicroStation can reproject the design data in the reference model. This is being done only temporarily; the changed data is not written back to the referenced file.
Because MicroStation knows the exact geographic location and orientation of both models, it can calculate the coordinates in the master model of any reference model point, as long as the geographic area of the reference model is within the useful range of the master model's geographic coordinate system.