⚠ Indicative tool only. Formulas and Table 5-2a/5-2b were checked directly against the standard's page images. The Variable Design Point Method was independently verified against API 650's own worked example (Appendix K, Example #2) — three real implementation bugs were found and fixed this way (radius units, corroded-vs-nominal thickness tracking, and the second-course interpolation formula), and the design-condition path now matches the standard's example exactly, course by course. One residual gap: the test-condition second-course convergence comes out slightly different from the example (~1% low) in a case we traced but couldn't fully resolve, since the example doesn't show a detailed iteration table for the test condition the way it does for design. The design condition typically governs shell thickness in practice and is exactly verified; treat test-condition VDP results for course 2+ with a bit more caution until this is pinned down further. One note on the material table: for EN 10025 S 355J0,J2 (non-K2), the source document's own SI table literally shows a thickness band of "16<t≤1½" — an inch fraction inside the mm table, almost certainly a units-carryover typo in the original publication (the very next row, S355J0,J2,K2, correctly shows "16<t≤40"). This tool uses 40 mm for that boundary rather than propagating the apparent error, and flags it here rather than silently "fixing" it. This is a design tool for new construction — for evaluating an existing tank's shell, use the Shell Thickness (API 653) calculator instead.