- According to Defense Directive 5111.11, the Director shall develop and coordinate net assessments of the standing, trends, and future prospects of U . S . military capabilities and military potential in comparison with those of other countries or groups of countries in order to identify emerging or future threats or opportunities for the United States.
- This reflects the fact that the system is gauge invariant ( in general, absent some symmetry, any choice of a curvilinear coordinate net on the same system would correspond to a numerically different solution . ) A " gauge fixing " is needed, i . e . we need to impose 4 ( arbitrary ) constraints on the coordinate system in order to obtain unequivocal results.