A common language
The IAEA specifies that VSMOW2 and SLAP2 are directly calibrated against the primary materials VSMOW and SLAP. These references support the comparability of reported hydrogen and oxygen isotope data.
How we interpret delta
A δ²H value describes a relative deviation from a reference standard. It must not be interpreted as an absolute concentration in ppm. A result is easier to interpret when the scale used is explicitly stated.
What we look for in a document
We note the reference materials, the scale, the unit, and the uncertainty. If we cite the result in an article, we retain this information; otherwise, the figure may lose precisely the context that renders it meaningful.
Why the delta value requires a reference
A relative deviation is meaningless without the reference value to which it is expressed. In its standard form, delta compares the isotopic ratio of the sample with that of the reference: δ = R_sample / R_reference − 1. When reported in ‰, the expression is multiplied by 1,000. A negative result indicates a ratio lower than that of the reference, not a negative quantity of deuterium. This interpretation is essential for correctly reading graphs and tables.
The common reference does not eliminate all differences.
Using the same scale facilitates comparison, yet a complete report must also describe how the laboratory arrived at the result. Calibration and intermediate verification are distinct from the name of the scale. If two documents report the same sample differently, we first examine the definitions and analytical conditions. We do not automatically select the value with more decimal places. For practical context,the article on laser analysistraces the steps from sample to report.
Documentation: the institutional source listed below. Questions and recommended readings are those of the publication, not statements by the cited institution.
IAEA · VSMOW2 ↗Published on 12 September 2026. Documented updates on 13 September 2026. Information on events may be updated by organizers.
