Equations for calculating delta values incorporating different
H3+ values are given in:

T. B. Coplen, Normalization of oxygen and hydrogen isotope data,
Chem. Geol. 72, 293-297 (1988).

Coplen, Wildman, and Chen, Improvements in the Gaseous Hydrogen-
Water Equilibration Technique for Hydrogen Isotope Ratio Analysis,
Anal. Chem., 910-912 (1991).

In fact, setting the H3+ to zero is required to get the best data
when analyzing urine samples for d2H by H2 equilibration using a
Finnigan 251 mass spectrometer at Phoenix, National Institutes of
Health (I. Harper).  Calculation of final d2H is performed by off
line evaluation.