SQUARE — is it square?

Phone-sensor measuring tools for home projects: find studs by magnetometer, level and plumb with a live camera overlay, compute true corner angles from a photograph, lay out repeat spacing, and capture cut angles for the saw. Offline-first PWA. Zero runtime dependencies. No network, no accounts, no analytics — it works in airplane mode in a crawlspace.

Every displayed number carries a unit and either a ± or a confidence state. The app would rather refuse than guess; see the Honesty Charter in kit/SPEC.md §15.

Deploy

Two-line path:

1. npm ci && npm run build
2. Drag dist/ onto Netlify Drop — or connect this repo and let the committed netlify.toml drive the build.

No environment variables, no API keys, no build secrets. The Permissions-Policy header in netlify.toml is what lets the browser expose the sensors — if sensors are dead on the deployed site and fine locally, check that header first.

Deploy status: not yet live. This build environment's network policy blocks Netlify's upload endpoints (verified: CONNECT 403 at the egress proxy for api.netlify.com and the MCP upload host), so the deploy could not be performed from inside the build session. Either path above works from any normal machine — or connect this repo in the Netlify UI (pick branch claude/ultrathink-build-kit-setup-v0ooqv or merge it first); the committed netlify.toml needs no configuration. After deploying, replace this block with the live URL.

Raw magnetometer on Android (Tier A / FIELD)

Chrome ships the raw magnetometer behind a flag:

1. Open chrome://flags/#enable-generic-sensor-extra-classes
2. Set Generic Sensor Extra Classes to Enabled
3. Restart Chrome, open the app, open SCAN.

Without the flag (and on iOS, always), SCAN runs in heading-deflection mode (PROXY badge, confidence capped) or manual mode — the app tells you which tier you're on and why.

Develop

npm ci
npm run dev          # local dev server
npm test             # full suite (unit + property + fixtures)
npm run verify:fixtures   # replay the trace corpus through the real pipeline
npm run build        # typecheck + build + generate service worker
npm run preview      # serve the built artifact

The math is implemented in-repo and test-first — see tests/unit/. Three load-bearing tests are frozen and predate their implementations (miter-canonical, zero-crossing, angle-solver-groundtruth); if one fails, the algorithm is wrong, not the test.

Sensor traces in tests/fixtures/ (format: tests/fixtures/SCHEMA.md) drive the regression suite, the replay harness (?replay=<fixture-id>), and the in-app DEMO walkthroughs — the same files, so the tutorials cannot drift from tested behavior.

Documentation

• PLAN.md / DECISIONS.md — plan of record and ADRs
• docs/PHYSICS.md — every formula, axis convention, and derivation
• docs/ACCURACY.md — honest measured accuracy per feature per calibration state
• docs/FIELD-TEST.md — the 90-minute real-wall validation protocol
• kit/ — the source spec and brand kit (reference, not shipped)

Fonts

DDC Hardware (Lost Type Co-op) ships self-hosted with two patched glyphs (µ, ′). The woff2 files are pinned byte-for-byte by the test suite — do not re-subset them. They are licensed for this site only: not for download, not for redistribution. See kit/LICENSE-NOTES.md.