These numbers define our universe. c = 299792458 m/s is exact by definition. So are µ₀ = 4π × 10⁻⁷ and ε₀ = 1/(µ₀c²). Yet G still carries 4.7 × 10⁻⁵ relative uncertainty, while α is known to 2.3 × 10⁻¹⁰. CODATA’s 2014 least-squares adjustment fused every precise measurement into one self-consistent set. Planck’s h, the elementary charge e, Avogadro’s N_A and the rest form the silent scaffolding of quantum mechanics, electromagnetism and statistical physics. Without them GPS clocks drift, quantum computers cannot calibrate, and the Boltzmann constant cannot convert temperature into energy. The constants are not decorations; they are the fixed points against which every physical law is measured. Which of these values most shapes the technology you build or study?