What the cone determines

convention of this note. All endpoint estimates below are in one declared coordinate frame $T_D$. The normalized null slope is one in those coordinates. A positive comparison unit $\ell$ is used to make endpoint errors dimensionless. Its numerical normalization is declared, not derived.

If clocks, rods, tick durations, or physical units are introduced, their calibration and correspondence to these coordinates belong to the transport realization. Classification does not fix them. A Lorentzian quadratic form on one affine carrier is also not a constructed metric field on a manifold.