  Recently (arXiv:1101.0973), it has been pointed out by us that the possible
variation in any source (S) specific elemental isotopic (viz. 2H/1H) abundance
ratio SR can more accurately be assessed by its absolute estimate Sr [viz. as
(Sr - DR), with D as a standard-source] than by either corresponding
measured-relative (S/W-DELTA) estimate ([Sr/Wr] - 1) or
DELTA-scale-converted-relative (S/D-DELTA) estimate ([Sr/DR] - 1). Here, we
present the fundamentals behind scale-conversion, thereby enabling to
understand why at all Sr should be the source- and/ or variation-characterizing
key, i.e. why different lab-specific results should be more closely comparable
as absolute estimates (SrLab1, SrLab2) than as desired-relative (S/D-DELTALab1,
S/D-DELTALab2) estimates. Further, the study clarifies that: (i) the
DELTA-scale-conversion (S/W-DELTA into S/D-DELTA, even with the aid of
calibrated auxiliary-reference-standard(s) Ai(s)) cannot make the estimates (as
S/D-DELTA, and thus Sr) free of the measurement-reference W; (ii) the employing
of (increasing number of) Ai-standards should cause the estimates to be rather
(increasingly) inaccurate and, additionally, Ai(s)-specific; and (iii) the
S/D-DELTA-estimate may, specifically if S happens to be very close to D in
isotopic composition (IC), even misrepresent S; but the corresponding Sr should
be very accurate. However, for S and W to be increasingly closer in IC, the
S/D-DELTA-estimate and also Sr are shown to be increasingly accurate,
irrespective of whether the S/W-DELTA-measurement accuracy could thus be
improved or not. Clearly, improvement in measurement-accuracy should ensure
additional accuracy in results.
