This paper develops a structural account of physical constants within the Quantized Dimensional Ledger (QDL), a closure-based dimensional framework in which physical quantities are represented by integer ledger charges in a 3L + 2F basis and judged by dimensional closure rather than by dimensional homogeneity alone. The central claim is that some constants function as structural interface objects: they mediate lawful dimensional passage between otherwise distinct sectors of representation, especially between action, field content, scale relations, calibration, and reportable measurement structure. The paper introduces a role-based classification of constants, dividing them into primitive closure anchors, interface-mediating constants, emergent ledger ratios, and effective bridge parameters. It then strengthens the metrological content of that classification by relating Quantum Measurement Units (QMUs) to SI-stabilized constants after the 2019 SI redefinition, distinguishing exact definitional anchors from adjusted empirical constants and emergent ratios, and giving explicit ledger assignments for the main worked examples. Those examples treat Planck’s constant as an action-measurement bridge, the gravitational constant as a geometry-matter bridge, and vacuum impedance and the Rydberg constant as emergent ledger ratios whose interpretation depends in part on normalization conventions. A final witness example exhibits a closure-defective dimensional relation and shows how insertion of a lawful interface constant restores admissibility. The paper does not claim numerical derivation of known constants or completion of a unified field theory. Its claim is narrower and metrological: within QDL, physical constants can be classified by the structural work they perform in preserving dimensional closure across theory and measurement. In this way, the paper extends the QDL Unified Admissibility Theory programme into the ontology of constants, SI-linked measurement structure, and closure-governed calibration and reporting.
James D. Bourassa (Sun,) studied this question.