This paper presents the canonical structural diagram for Tier-4 within the Paton System. Tier-4 represents the observational interface through which admissible systems become legible to an observer. Previous papers describing the Datum Interface, the Knowledge Interface, Mirror Architecture, and the Universal Knowledge Interface are shown to be structurally equivalent expressions of the same interface layer. The paper consolidates these descriptions into a single canonical diagram and explanatory framework. The goal is not to introduce a new mechanism but to stabilise the interpretation of Tier-4 across domains by providing a unified visual representation. Within the Paton System architecture, Tier-4 sits directly above the admissibility gate and forms the boundary between unobserved admissible structure and observable structural relations. The canonical Tier-4 diagram demonstrates how observation, reference, and reflection emerge from the same structural interface. By consolidating the Datum Interface, Knowledge Interface, Mirror Architecture, and Universal Knowledge Interface into a single structural representation, the paper clarifies the role of Tier-4 as the universal observation layer across physical, computational, biological, and cognitive systems.
Andrew John Paton (2026) studied this question.