Big bang production of deuterium is the best indicator of the baryon d
ensity; however, only the present abundance of D is known (and only lo
cally) and its chemical evolution is intertwined with that of He-3. Be
cause Galactic abundances are spatially heterogeneous, mean chemical-e
volution models are not well suited for extrapolating the pre-solar D
and He-3 abundances to their primeval values. We introduce a new appro
ach which explicitly addresses heterogeneity by statistically tracing
the history of the pre-solar material back to its primeval beginning.
We show that the decade-old concordance interval eta approximate to (2
-8)x10(-10) based on D and He-3 is well founded.