After a brief comparison with earlier
work (Section 5.1) we offer in
Section 5.2
an assessment of the major
uncertainties in our budget at low redshift, with emphasis on the
more indirect arguments we hope constrain the budget of baryons
in forms that are unobservable in practice. We review the test
from the theory for the origin of the light elements
in Section 5.3, and in
Section 5.4 we compare
these results with measurements of the diffuse baryons at
z 
3. Some concluding
remarks are offered in Section 5.5.