The Born Rule: Index and Fixation. Harmonic Mass and Stable Records.

The Born rule connects squared amplitudes with the frequencies of recorded outcomes. This preprint constructs that connection through two explicit mechanisms: the square is a lattice index; probability is a fixation share. Complex multiplication on a lattice of rank two produces a contact layer whose cardinality equals the squared modulus of the register content. Loading one unit at each contact turns this arithmetic count into conserved mass. Fair transfers redistribute the units until a single contact survives. A bounded-martingale argument then gives each contact a winning probability equal to its initial share. Within the specified interaction class, the resulting Born law is exact, holds from every initial clock address, and is independent of the encounter schedule, provided fairness and completion are maintained. Polarization of the contact count also recovers the Hermitian geometry of the register. A single object, harmonic mass, connects the outcome law to the arrow of fixation. Its normalized coordinates give the conditional probabilities of future records, while its positive support can only shrink: an excluded alternative cannot return during the same run. The paper develops finite certificates for this structure, including sectorwise balance and a characterization of robustness under causal changes of the interaction parameter. Protected block outputs yield the sequential Born–Lüders law. Rational generalized measurements admit exact integer dilations and use the same fixation mechanism. Quantitative continuity gives a unique extension to arbitrary finite-dimensional states and measurements; controlled truncations extend the probability law to normal states on separable Hilbert spaces, including continuous spectra. The construction also makes the resources of recording calculable. Exact transfer costs, bounds on deviations from the Born law, retention times, and slow recording-error dynamics are derived. A temporal certificate reconstructs contact masses from activity measurements independently of winner frequencies. Developed within the Theory of Structural Articulation, the paper provides a complete finite event-source realization and a criterion for transferring its law to other physical carriers. Application to a particular recording process requires independent verification of contact loading, interaction balance, completion, and protection of the recorded block.