The Paton System proposes that system continuation depends on structural admissibility under governing constraints. While admissibility conditions determine whether continuation is permitted, these conditions must be evaluated relative to a structural reference position. This paper clarifies the role of the Datum Interface as the layer within the Paton System where system states become observable and structurally evaluable. The Datum Interface does not generate system behaviour or impose constraints; instead, it provides the reference position from which admissibility conditions can be assessed. This clarification strengthens the Tier-4 placement within the Paton System architecture and explains how different scientific disciplines implicitly operate relative to such a structural datum. Across scientific disciplines, systems are evaluated relative to reference positions. Physics evaluates configurations relative to frames of reference, control theory evaluates states relative to defined state spaces, optimisation evaluates solutions relative to feasibility regions, and biology evaluates organism viability relative to environmental constraints. Although these fields employ different terminology, they perform structurally equivalent operations. Within the Paton System architecture, the Datum Interface occupies Tier-4 and functions as the structural location where system states become evaluable relative to admissibility conditions defined at Tier-3. By clarifying this layer, the paper strengthens the architectural coherence of the Paton System and explains how admissibility evaluation operates across domains.
Andrew John Paton (Wed,) studied this question.