See SourceSystem.
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I think mutual references without explanations explaining the differences are a waste of time, & disk space.  If someone has an explanation of SystemOfOrigin, please erase my entry here & put in your explanation.  Also, if in the course of doing that you also reference SystemOfReference, then you will have accomplished a great service to those like me who are trying to understand these concepts.  TerryLeeMoore 27 Jun 02