Consistency can be evaluated with the so-called sum rules, which are integrals of the optical constants of a material in the full spectrum. Standard sum rules can help detect inconsistency of the optical constants but cannot say what specific spectral range(s) is responsible of such inconsistency. A new sum-rule procedure has been developed to evaluate the consistency at each specific spectral range with the use of window functions  and .
Consistency evaluation parameter ζ of Al optical constants through the spectrum. Optical constants are considered consistent when ζ stands within ±0.005. The fluctuations of ζ away from the acceptable range in the ~40-150 eV range and above ~4400 eV are attributed to inconsistency of the optical constants mainly at the indicated spectral ranges.
Consistency evaluation parameter ζ of SiO2 optical constants. Five sum rules were used, which includes the indicated energy power. Parameter ζ comfortably stands within the ±0.005 limits in the whole spectral range for all five sum rules, which indicates that the optical constants are locally consistent in this wide spectrum. The exception is E2-sum rule in the limit of high-energy windows, where it diverges, what is attributed to limited precision in sum-rule calculations.