Physics does not have hundreds of independent constants. It has a small set of headwaters and a long braid of consequences. This map draws the ancestry honestly: at the top sit the seven constants the 2019 SI fixed exactly, by decree (ΔνCs, c, h, e, kB, NA, Kcd) beside the four great measured springs no committee can fix — the fine-structure constant α, the electron and proton masses, and Newton's G. Everything below is woven: μ₀ from α, h, e, c; the Rydberg from α, mₑ, c, h; the Stefan–Boltzmann constant entirely from k_B, h, c — which is why it is now exact.
Each derived node's card recomputes its formula live from the headwater values and compares against the CODATA 2022 recommended value — agreement is displayed, and the page fails its own checks if any weave breaks.
For 130 years a platinum-iridium cylinder in a Sèvres vault was the kilogram; h was something you measured against it. On 20 May 2019 the SI turned the arrows around: now h is exact by definition and the kilogram is derived. The ⇄ Pre-2019 SI button replays the old world: watch the units turn gold (they were the bedrock), h, e, k_B, N_A turn dashed (they were measured), and μ₀ snap to the exact 4π×10⁻⁷ it enjoyed before it was set free — it is now a measured quantity carrying α's uncertainty.
Which constants are "fundamental" is partly convention — the SI's choice of seven is metrological, not metaphysical (Duff, Okun and Veneziano famously disagreed on whether the count is 3, 2 or 0). This map shows the SI's genealogy, with the measured springs kept visually distinct. Unit definitions shown with a single parent also lean on previously-defined units (the kilogram's definition uses the metre and second); the cards spell out the full chain. Proton and neutron masses are measured, not woven — QCD in principle predicts them from ΛQCD and quark masses, but not yet at metrological precision, so the honest arrow stops.
CODATA 2022 — Tiesinga, Mohr, Newell & Taylor, NIST, physics.nist.gov/constants · BIPM, SI Brochure, 9th ed. (2019), Appendix 3 · "The revision of the SI", Metrologia 56 (2019) · Duff, Okun & Veneziano, JHEP 03 (2002) 023 · Siblings: Dimension Space