Conciseness

The body is almost entirely executable code and dense reference tables with no explanation of concepts Claude already knows, but minor redundancy could be trimmed: the attitude-frame guidance is stated three times (prose, the frame table, and a second "Check available frames" snippet) and the accelerometer/gyro examples repeat near-identical print scaffolding. This fits 'efficient; minor instances of over-explanation that could be trimmed' rather than 'every token earns its place'.

Actionability

Every section is copy-paste-ready Swift covering the common case per sensor, including availability guards, update intervals, handler destructuring, and matching stop calls; tables give concrete values. This matches the fully-executable anchor and is not a 4 since no key detail is missing from the shown patterns.

Workflow Clarity

Setup (Info.plist, authorization) → availability gate → start → stop is clearly sequenced, availability guards act as inline checkpoints, and the Review Checklist plus WRONG/CORRECT Common Mistakes provide verification feedback. It falls short of 5 because there is no explicit error-recovery loop (validate → fix → retry) and the setup steps are not presented as an explicitly ordered flow; no destructive/batch cap applies since this is sensor reading.

Progressive Disclosure

Against the actual bundle, SKILL.md keeps core manager APIs inline and moves extended patterns (SwiftUI integration, batched sensors, headphone motion, water submersion) into a single clearly-signaled, one-level-deep references/motion-patterns.md with a descriptive link; navigation via Contents and section anchors is easy. This matches the score-5 anchor and is not a 4 since the split and signaling are already clean.

Specificity

The description enumerates ten concrete capability areas ("accelerometer, gyroscope, magnetometer, device-motion, pedometer, activity-recognition, altitude, headphone motion, batched high-frequency workout motion, and water-submersion/depth data") with no vague filler, matching the anchor for multiple specific concrete actions with comprehensive coverage. It cannot be below 5 since coverage of the Core Motion surface is exhaustive and every action named is concrete.

Completeness

It explicitly answers both questions: the first sentence states what the skill does (access specific Core Motion data types) and the second gives an explicit "Use when..." clause with concrete trigger phrases, directly matching the score-5 anchor example. It is not a 4 because the when-clause is already explicit and specific rather than improvable.

Trigger Term Quality

The when-clause uses natural phrases users would actually say: "reading device sensors", "counting steps", "detecting walking/running/driving/cycling", "tracking altitude", "AirPods head tracking", "watchOS dive/depth features". Only niche synonyms (e.g., workout/exercise tracking) are missing, so it sits at the comprehensive-coverage anchor rather than the 'a few natural terms missing' level below.

Distinctiveness Conflict Risk

The Core Motion sensor niche (accelerometer/gyro/device-motion) is clear and mostly distinct, but "counting steps" and "detecting walking/running" could plausibly route to a closely related HealthKit or fitness skill, which is minor overlap risk — the score-4 anchor. It is not 5 because of that adjacent-framework overlap; not 3 because the trigger set is firmly sensor-hardware oriented and unlikely to mis-fire broadly.