Offline-first Android pocket toolset: a trustworthy level, angle meter, and calibrated screen ruler (Pro). Kotlin + Jetpack Compose, single module, no backend.

BRIEF.md — the authoritative v1 product & technical brief
AUDIT.md — audit of the brief; the amendments it lists are incorporated
resources/ — concept board (visual direction)

Building

Open in Android Studio, or:

./gradlew assembleDebug        # build
./gradlew testDebugUnitTest    # measurement-math unit tests

Scaffold status

The project skeleton follows BRIEF.md §Sensor and measurement architecture. Implemented and tested:

core/sensors — sensor selection (game rotation vector → gravity → low-passed accelerometer), device-frame gravity stream, and the pure measurement math: orientation mapping, two-sample per-mode calibration (derived in angle space, applied in vector space so it stays correct away from zero), EMA smoothing, lock hysteresis/dwell/debounce, display deadband, placement validity, and the sensor-vector contract (all sources emit device-frame world-up; flat = +9.81 on Z, pinned by SensorContractTest). All unit-tested.
core/settings — DataStore preferences and per-mode calibration persistence.
core/billing — entitlement interface with a stub (free-tier) implementation.
feature/level, feature/angle — live numeric scaffolds wired to the real sensor pipeline, with manual Surface|Edge selection, placement-validity hints, lock state (locked label states the tolerance so it can never contradict the rounded readout), and directional hold-to-zero (vector reference, not magnitude subtraction).
feature/ruler, feature/tools — static placeholders.

Not yet implemented (deliberately — see TODO markers):

The tactile vial visuals and the spring-animated display value (value 3 of 3 in the brief); scaffold screens render the deadbanded stable value directly.
Guided calibration flow UI (math and persistence are done).
Edge-mode readout counter-rotation on the portrait-locked activity.
Play Billing implementation of ProEntitlementRepository.
Screen ruler measurement UI and per-display scale persistence.
Audio cue, reduced-motion behaviors, preferences UI.