The Admiralty Code's six-level scales sit in the same information-theoretic lineage as the question of how many categories absolute judgment can carry — Miller (1956) through Bendig (1954) to Samet (1975)

cross-time-bridgeinformation-theorypsychophysicsintelligence-tradecraftsource-evaluationadmiralty-coderating-scalesepistemics

The vault's two-axis source-model cluster answered how many axes a source rating needs and whether the axes hold apart. It never asked the orthogonal question: why does each axis have six levels? The answer runs backward through a citation chain into information theory, and it is not intelligence doctrine.

The trace: Samet (1975) argued the Admiralty Code's scales were too coarse and cited Bendig (1954) — "more information can be transmitted by a rating scale that uses nine categories rather than five." Bendig's rating-scale-length work belongs to the tradition Miller (1956) crystallized as the channel capacity of absolute judgment: the observer, treated as a communication channel, saturates around seven-plus-or-minus-two distinguishable categories on a single dimension. A source-rating scale's rung count is therefore governed by the same ceiling that governs pitch and loudness judgments.

Two things make this a bridge worth a note rather than a footnote. First, it is cross-time: 1956 psychophysics underwrites a 1975 Army report that grades reports on scales still carried in NATO STANAG 2511 / AJP-2.1 and re-derived by 2025 retrieval research — none of which cites the psychophysics. Second, it is a different axis of analysis from the existing cluster: that cluster is about the two-axis structure and its leak; this is about scale length within an axis. It also bears on the open source-tier design question, adding granularity-per-axis as a third design dimension alongside fuse-vs-split.

The lineage is a citation trace — Samet cites Bendig, Bendig sits in Miller's tradition — not evidence that whoever set the Admiralty Code's six levels was reading Miller. The scales' actual design provenance is not established here.