diff --git a/README.md b/README.md
index 3fe2b80..0e7d302 100644
--- a/README.md
+++ b/README.md
@@ -1,209 +1,59 @@
-# Xiaomi Vela Hello World for Watch S4
+# CALCULATOR — round-screen calculator for Xiaomi Watch S4
-This is the smallest practical Xiaomi Vela JS watch application. It shows two centered lines on a round black screen:
+A calculator laid out for the circular display: tapered key rows that follow the
+chord of the round screen, large touch targets, high-contrast keys (#3a3a3e on #000).
+Supports chained operations, percent, sign toggle, decimals, and divide-by-zero
+error recovery.
+
+**Status: WORKING ON WATCH** (user-confirmed through v1.2; layout improved through 1.6).
+
+## Usage
+
+- Tap keys to compute; `AC` clears all
+- `%` divides the display by 100 (plain semantics — 200+10% = 200.1)
+- Back button exits (no onBackPress interception — intercepted back made the
+ button feel dead on a single-page app)
+- Crown does nothing (unsupported API on Vela); the original crown-selection
+ scheme was abandoned for a directly-tappable list layout
+
+## Round-screen layout (the interesting part)
+
+- Short viewport (~300px) so rows never exceed the circle chord
+- NO vertical margins on list-items (spacing baked into height — CSS/JS drift bug)
+- Top/bottom spacer items so first/last keys can center in the viewport
+- Focus = round((scrollY + KEYS_H/2 − ITEM_H/2 − PAD)/ITEM_H); re-centered after
+ every press via scrollTo
+- Geometry + contrast assertions live in `tests/visual.cjs` (parses the .ux)
+
+## Project layout
```text
-Hello World!
-Xiaomi Watch S4
+src/
+├── app.ux, manifest.json # com.example.hellovela identity (preserved for updates)
+├── common/icon.png # 192×192 circular icon
+└── pages/index/index.ux # keys list + display + state machine
+tests/
+├── page.cjs # state machine: driven via press(key) sequences
+└── visual.cjs # parsed-from-source geometry/contrast contracts
```
-It compiles entirely from a Linux terminal. Xiaomi AIoT-IDE is not required.
-
-## 1. What you need
-
-- A 64-bit Linux system
-- Node.js and npm
-- OpenSSL, but only if you want a signed release package
-- Internet access for the first `npm install`
-
-Node.js 20 LTS is a conservative choice. The included project has also been build-tested with Node.js 24 and npm 11.
-
-On Ubuntu or Debian, install the basic tools:
-
-```bash
-sudo apt update
-sudo apt install -y curl openssl
-```
-
-Install Node.js using your preferred package manager or a version manager such as `nvm`. Confirm that it works:
-
-```bash
-node --version
-npm --version
-```
-
-## 2. Understand the tiny project
-
-```text
-xiaomi-vela-s4-hello-world/
-├── package.json
-├── README.md
-├── sign/
-└── src/
- ├── app.ux
- ├── manifest.json
- ├── common/
- │ ├── icon.png
- │ └── icon.svg
- └── pages/
- └── index/
- └── index.ux
-```
-
-- `package.json` installs Xiaomi's command-line build tool and defines the build commands.
-- `src/manifest.json` defines the package, icon, watch target, design width, and start page.
-- `src/app.ux` contains application lifecycle hooks.
-- `src/pages/index/index.ux` contains the UI and its styles.
-- `sign/` is where release certificate files go. Keep private keys private.
-
-Vela `.ux` files resemble small single-file web components. A page may contain `template`, `style`, and `script` blocks. This Hello World page needs only `template` and `style`.
-
-## 3. Compile a debug RPK without Xiaomi's IDE
-
-Open a terminal in the project folder and run:
-
-```bash
-npm install
-npm run build
-```
-
-The important output is created under `dist/` and ends in `.debug.rpk`:
-
-```bash
-find dist -maxdepth 1 -type f -name '*.rpk' -print
-```
-
-The `build/` directory contains intermediate generated files. You normally do not edit either `build/` or `dist/`.
-
-To include a separate source map while debugging:
-
-```bash
-npm run build:source-map
-```
-
-To see every compiler option supported by your installed toolkit:
-
-```bash
-npm run help
-```
-
-## 4. Create a signed release RPK
-
-The release builder expects these two files:
-
-```text
-sign/private.pem
-sign/certificate.pem
-```
-
-Generate a local development certificate from the project root:
-
-```bash
-openssl req \
- -newkey rsa:2048 \
- -nodes \
- -keyout sign/private.pem \
- -x509 \
- -days 3650 \
- -out sign/certificate.pem \
- -subj '/CN=Hello Vela Development/O=Example/C=US'
-```
-
-Then compile the release package:
+## Build & test
```bash
+npm ci
npm run release
-find dist -maxdepth 1 -type f -name '*.release.*.rpk' -print
+node tests/page.cjs
+node tests/visual.cjs
```
-Do not commit or share `sign/private.pem`. If a companion Android application communicates with the watch app, Xiaomi's wearable integration may require matching signing identity; changing certificates later can also prevent an update from being accepted as the same app.
+## Install
-## 5. Change the app
+Side-load via AstroBox. Releases:
+https://gitea.oimcloud.myaddr.tools/codex-bot/vela-calculator
-Edit `src/pages/index/index.ux`. For example, replace:
+## Bug history worth knowing (all caught by the stale-test TDD pass)
-```xml
-Hello World!
-```
-
-with:
-
-```xml
-My first app
-```
-
-Then rebuild:
-
-```bash
-npm run build
-```
-
-When publishing an update, increase `versionCode` in `src/manifest.json`. Also update `versionName` when you want the visible version string to change.
-
-## 6. Important Vela rules
-
-- A template must have exactly one root element.
-- Visible text must be inside a `` component.
-- Vela uses flex layout, but its CSS support is smaller than a browser's CSS support.
-- Package names should use reverse-domain form, such as `com.yourname.hello`.
-- `designWidth: 480` lets Vela scale the 480-pixel design to the physical display.
-- APIs such as sensors, storage, network, or vibration must usually be declared in the manifest's `features` array before use. This Hello World app requests no APIs.
-
-## 7. Installing on a real Watch S4
-
-Compilation and installation are separate. The terminal workflow above reliably creates the `.rpk`; transferring it to a physical watch depends on the exact Watch S4 model, firmware region, Mi Fitness version, and whether developer or debugging access is enabled for that firmware.
-
-Do not treat the `.rpk` as an Android APK, and do not flash random firmware. Use Xiaomi's supported wearable deployment route for your device/account. Some retail or global firmware builds do not expose the same development or sideload controls as Chinese developer setups.
-
-## 8. Troubleshooting
-
-### `aiot: command not found`
-
-Always run the local tool through npm:
-
-```bash
-npm install
-npm run build
-```
-
-Do not rely on a global `aiot` installation.
-
-### Dependency installation fails
-
-Clear only this project's installed dependencies and retry:
-
-```bash
-rm -rf node_modules
-npm install
-```
-
-If you use a company proxy, configure npm for that proxy instead of disabling TLS verification.
-
-### No `.rpk` appears
-
-Read the first compiler error, then verify:
-
-```bash
-npx aiot build -h
-find src -maxdepth 4 -type f -print
-```
-
-The required files are `src/manifest.json`, `src/app.ux`, and the routed page component.
-
-### Release build says signing files are missing
-
-Run the OpenSSL command in section 4 and confirm:
-
-```bash
-test -s sign/private.pem && test -s sign/certificate.pem && echo 'Signing files exist'
-```
-
-## Official references
-
-- Xiaomi Vela JS documentation:
-- Project structure:
-- Manifest configuration:
-- Compiler parameters:
-- UI introduction:
-
-The project intentionally uses only the public `aiot-toolkit` command-line package. It does not require Xiaomi AIoT-IDE.
+- `fresh` never initialized → first digit appended to '0' ('01')
+- `=` with no pending op zeroed the display
+- Operators didn't auto-evaluate pending ops (2+3×4 gave 12, not 20)
+- Repeated `=` didn't re-apply the last op (2+3== gave 5, not 11)