Every distance and speed scales 1:1 with one absolute anchor — the 2.70 m axle spacing (operator-confirmed nominal/design value, with no field calibration). Two geometry cross-checks (end-bogie span 17.37 m vs the operator's 17.40 m = 0.17%; interior-bogie gaps ~1.5% short) close to a ~1–1.5% self-consistency / shape-closure residual — but these are anchor-proportional, so they confirm constant-speed timing and consist proportions, NOT the absolute metre. The on-site sleeper line (~0.67 m, inside the operator's estimated 0.60–0.80 m range) is a one-sided plausibility cross-check against the operator's sleeper-pitch range — not an independent calibration of the metre; its band is too wide to tighten the scale. So uncalibrated absolute distance / speed / wavelength carry ~5–12% (one pinned figure, an engineering estimate — not a GUM-propagated budget) until a field hammer-test / trolley run calibrates the anchor. Wheel diameter 0.89 m is the published CIVIA-465 spec (assumed; no per-unit value). Speed is derived from these, not measured — a commodity axle counter quotes ~0.2% traceable; we do not claim a traceable budget. Acquisition is fixed at 2048 Hz (Nyquist 1024 Hz); the impact/flat-wheel envelope is band-limited to 300–900 Hz, so flat-impact content above ~1 kHz is not observable at this rate and the delivered acquisition's anti-alias response is unstated — the impact screen sees a band-limited proxy, not the full transient. The health indexes (AHI / THI / FHI, 0–1) are relative, worst-first ranking scores — NOT metrological measurements, and they carry no GUM uncertainty budget (the 2-decimal display ranks, it does not measure). A site hammer-test / trolley run would convert these to absolute, calibrated figures — target <1% absolute against a surveyed sleeper pitch / stock drawing / instrumented trolley (roadmap).