TriboTech ApS
Expert Tribology Consultancy
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Compute the Viscosity Index of a lubricant from its kinematic viscosity at 40 °C and 100 °C, per ASTM D2270-24 — Section 5 primary method (Table 1 with linear interpolation; Eqs 1–2 above 70 mm²/s).
Calculated per ASTM D2270 (technically equivalent to ISO 2909).
Viscosity Index reproducibility is ±2 VI units (ASTM D2270 Table X3.1); differences smaller than this are within method noise.
v₄₀ = 73.30, v₁₀₀ = 8.86 → VI = 92
v₄₀ = 22.83, v₁₀₀ = 5.05 → VI = 156
v₄₀ = 53.47, v₁₀₀ = 7.80 → VI = 111
Implementation follows ASTM D2270-24 Section 5, the standard's primary method: L and H are looked up in Table 1 (with linear interpolation for unlisted values) for 100 °C viscosities up to 70 mm²/s, and computed from Eqs 1–2 above that. The Appendix X2 quadratics are retained as an internal cross-validator — on conflict, Section 5 is normative (X2.1.1). VI is rounded per ASTM E29 (exact halves to the nearest even number), and reproducibility is ±2 VI units (Table X3.1). ISO 2909 uses the same reference-oil system, Table 1 and equations, so ISO-referencing users get the same answer.