diff --git a/samples/hp48/index.html b/samples/hp48/index.html
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+<!doctype html>
+<html lang="en">
+<head>
+  <meta charset="utf-8">
+  <meta name="viewport" content="width=device-width, initial-scale=1">
+  <title>HP48-style RPN Calculator</title>
+  <style>
+    :root {
+      --body: #d8d8d8;
+      --panel: #202020;
+      --panel-2: #2b2b2b;
+      --screen: #d8e7b8;
+      --screen-text: #1b2a12;
+      --screen-dim: #5b6f45;
+      --key: #3a3a3a;
+      --key-text: #f2f2f2;
+      --accent: #8cff6d;
+      --border: #111;
+    }
+
+    * { box-sizing: border-box; }
+
+    body {
+      margin: 0;
+      font-family: Arial, sans-serif;
+      background: linear-gradient(180deg, #efefef, var(--body));
+      color: #111;
+    }
+
+    .wrap {
+      max-width: 980px;
+      margin: 0 auto;
+      padding: 24px;
+    }
+
+    .calc {
+      background: linear-gradient(180deg, #2f2f2f, #1f1f1f);
+      border: 1px solid #111;
+      border-radius: 20px;
+      padding: 18px;
+      box-shadow: 0 18px 48px rgba(0, 0, 0, 0.25);
+    }
+
+    .brand {
+      color: #fafafa;
+      display: flex;
+      justify-content: space-between;
+      align-items: baseline;
+      margin-bottom: 12px;
+      gap: 12px;
+    }
+
+    .brand h1 {
+      margin: 0;
+      font-size: 18px;
+      letter-spacing: 0.06em;
+    }
+
+    .brand small {
+      color: #c9c9c9;
+    }
+
+    .screen {
+      background: linear-gradient(180deg, #dbe8b8, var(--screen));
+      color: var(--screen-text);
+      border: 2px inset #8aa36b;
+      border-radius: 10px;
+      padding: 14px;
+      min-height: 190px;
+      font-family: "Courier New", monospace;
+      display: grid;
+      grid-template-rows: auto auto 1fr;
+      gap: 10px;
+    }
+
+    .screen-top {
+      display: flex;
+      justify-content: space-between;
+      gap: 12px;
+      font-size: 12px;
+      color: var(--screen-dim);
+    }
+
+    .stack {
+      border-top: 1px solid rgba(27, 42, 18, 0.35);
+      padding-top: 10px;
+      line-height: 1.5;
+      font-size: 18px;
+      white-space: pre-wrap;
+    }
+
+    .stack-line {
+      display: grid;
+      grid-template-columns: 26px 1fr;
+      gap: 8px;
+    }
+
+    .stack-line .label {
+      text-align: right;
+      color: var(--screen-dim);
+    }
+
+    .hidden-input {
+      position: absolute;
+      left: -9999px;
+      width: 1px;
+      height: 1px;
+      opacity: 0;
+      pointer-events: none;
+    }
+
+    .input-row {
+      display: grid;
+      grid-template-columns: 1fr 150px;
+      gap: 12px;
+      margin-top: 14px;
+    }
+
+    input, select, button {
+      border-radius: 10px;
+      border: 1px solid #000;
+      font: inherit;
+    }
+
+    input, select {
+      padding: 12px 14px;
+      background: #f7f7f7;
+      color: #111;
+    }
+
+    .panel {
+      margin-top: 14px;
+      background: rgba(255, 255, 255, 0.04);
+      border: 1px solid rgba(255, 255, 255, 0.08);
+      border-radius: 14px;
+      padding: 14px;
+    }
+
+    .title {
+      color: #fff;
+      margin: 0 0 10px;
+      font-size: 14px;
+      text-transform: uppercase;
+      letter-spacing: 0.08em;
+    }
+
+    .buttons {
+      display: grid;
+      gap: 8px;
+      grid-template-columns: repeat(auto-fit, minmax(92px, 1fr));
+    }
+
+    button {
+      padding: 12px 10px;
+      background: linear-gradient(180deg, #4a4a4a, var(--key));
+      color: var(--key-text);
+      cursor: pointer;
+      box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.08);
+    }
+
+    button:hover { filter: brightness(1.08); }
+    button:active { transform: translateY(1px); }
+
+    .status {
+      margin-top: 12px;
+      display: flex;
+      flex-wrap: wrap;
+      gap: 10px;
+      color: #ececec;
+      font-size: 13px;
+    }
+
+    .pill {
+      border: 1px solid rgba(255, 255, 255, 0.15);
+      border-radius: 999px;
+      padding: 5px 10px;
+      background: rgba(255, 255, 255, 0.05);
+    }
+
+    .error {
+      margin-top: 10px;
+      min-height: 20px;
+      color: #ff8a8a;
+      font-family: "Courier New", monospace;
+      font-size: 13px;
+    }
+
+    .hint {
+      color: #ddd;
+      margin-top: 10px;
+      font-size: 13px;
+      line-height: 1.5;
+    }
+  </style>
+</head>
+<body>
+  <div class="wrap">
+    <div class="calc">
+      <div class="brand">
+        <h1>HP48-style RPN</h1>
+        <small>powered by src/rpn-calculator.js</small>
+      </div>
+
+      <div class="screen" id="screen" tabindex="0" role="application" aria-label="HP48 style calculator screen">
+        <div class="screen-top">
+          <div>RPN stack</div>
+          <div id="modeLabel">deg</div>
+        </div>
+        <div id="stack" class="stack"></div>
+        <div id="display"></div>
+      </div>
+
+      <input id="input" class="hidden-input" type="text" autocomplete="off" aria-hidden="true" tabindex="-1">
+
+      <div class="input-row">
+        <div class="hint">Keyboard input is captured directly by the screen</div>
+        <select id="angleMode">
+          <option value="deg">Degrees</option>
+          <option value="rad">Radians</option>
+          <option value="grad">Grads</option>
+        </select>
+      </div>
+
+      <div class="status">
+        <div class="pill">inputValue: <span id="inputValueLabel"></span></div>
+        <div class="pill">isEditing: <span id="editingLabel"></span></div>
+      </div>
+
+      <div class="panel">
+        <div class="title">Stack</div>
+        <div class="buttons" id="stackButtons"></div>
+      </div>
+
+      <div class="panel">
+        <div class="title">Arithmetic</div>
+        <div class="buttons" id="arithButtons"></div>
+      </div>
+
+      <div class="panel">
+        <div class="title">Trigonometry</div>
+        <div class="buttons" id="trigButtons"></div>
+      </div>
+
+      <div class="panel">
+        <div class="title">Constants</div>
+        <div class="buttons" id="constButtons"></div>
+      </div>
+
+      <div id="error" class="error"></div>
+      <div class="hint">Use Enter to commit the current value. Buttons call <code>command(...)</code> directly, like a real RPN demo.</div>
+    </div>
+  </div>
+
+  <script src="../../src/rpn-calculator.js"></script>
+  <script>
+    const calc = new RpnCalculator({ angleMode: 'deg' });
+    const input = document.getElementById('input');
+    const screen = document.getElementById('screen');
+    const stackEl = document.getElementById('stack');
+
+    const displayEl = document.getElementById('display');
+    const errorEl = document.getElementById('error');
+    const inputValueLabel = document.getElementById('inputValueLabel');
+    const editingLabel = document.getElementById('editingLabel');
+    const modeLabel = document.getElementById('modeLabel');
+    const angleMode = document.getElementById('angleMode');
+
+    const groups = {
+      stack: ['enter', 'dup', 'drop', 'swap', 'clear'],
+      arithmetic: ['add', 'sub', 'mul', 'div', 'mod', 'pow', 'sqr', 'neg', 'sqrt', 'recip', 'log', 'ln'],
+      trig: ['sin', 'cos', 'tan', 'asin', 'acos', 'atan'],
+      const: ['pi', 'e'],
+    };
+
+    function labelFor(command) {
+      return ({ add: '+', sub: '−', mul: '×', div: '÷', pow: 'y^x', recip: '1/x', sqr: 'x²' }[command] || command);
+    }
+
+    function addButtons(container, commands) {
+      container.innerHTML = '';
+      commands.forEach((commandName) => {
+        const button = document.createElement('button');
+        button.textContent = labelFor(commandName);
+        button.addEventListener('click', () => execute(commandName));
+        container.appendChild(button);
+      });
+    }
+
+    function render() {
+    const stack = calc.stack;
+    const names = ['T', 'Z', 'Y', 'X'];
+    const lines = [];
+    for (let i = 3; i >= 0; i -= 1) {
+      const value = stack[i];
+      lines.push(`<div class="stack-line"><div class="label">${names[3 - i]}</div><div>${value !== undefined ? calc.formatNumber(value) : ''}</div></div>`);
+    }
+
+      stackEl.innerHTML = lines.join('');
+      displayEl.textContent = calc.isEditing ? `ENTERING: ${calc.inputValue}` : 'READY';
+      inputValueLabel.textContent = calc.inputValue || '∅';
+      editingLabel.textContent = String(calc.isEditing);
+      modeLabel.textContent = calc.angleMode;
+      angleMode.value = calc.angleMode;
+      errorEl.textContent = '';
+    }
+
+    function execute(name) {
+      try {
+        if (name === 'swap') {
+          if (calc.isEditing) calc.command('enter');
+          if (calc.stack.length >= 2) calc.swap(0, 1);
+        } else if (name === 'drop') {
+          if (calc.stack.length >= 1) calc.remove(0);
+        } else if (name === 'clear') {
+          calc.clear();
+        } else if (name === 'enter') {
+          if (calc.isEditing) calc.command('enter');
+        } else if (name === 'pi' || name === 'e') {
+          calc.command(name);
+        } else {
+          calc.command(name);
+        }
+        render();
+      } catch (error) {
+        errorEl.textContent = error.message;
+      }
+    }
+
+    function isInputChar(key) {
+      return /^[0-9a-fA-F.+\-]$/.test(key);
+    }
+
+    function focusScreen() {
+      screen.focus();
+    }
+
+    function syncInputFromState() {
+      input.value = calc.inputValue;
+    }
+
+    screen.addEventListener('keydown', (event) => {
+      try {
+        if (event.key === 'Enter') {
+          event.preventDefault();
+          if (calc.isEditing) {
+            calc.command('enter');
+            syncInputFromState();
+          }
+          render();
+          return;
+        }
+
+        if (event.key === 'Backspace') {
+          event.preventDefault();
+          if (calc.isEditing) {
+            calc.inputValue = calc.inputValue.slice(0, -1);
+            if (calc.inputValue === '') calc.isEditing = false;
+            syncInputFromState();
+            render();
+          }
+          return;
+        }
+
+        if (isInputChar(event.key)) {
+          event.preventDefault();
+          calc.input(event.key);
+          syncInputFromState();
+          render();
+          return;
+        }
+
+        const keyMap = {
+          '+': 'add',
+          '-': 'sub',
+          '*': 'mul',
+          '/': 'div',
+          '%': 'mod',
+          '^': 'pow',
+        };
+
+        if (keyMap[event.key]) {
+          event.preventDefault();
+          calc.command(keyMap[event.key]);
+          render();
+        }
+      } catch (error) {
+        errorEl.textContent = error.message;
+      }
+    });
+
+    screen.addEventListener('click', focusScreen);
+    window.addEventListener('load', focusScreen);
+
+    angleMode.addEventListener('change', (event) => {
+      calc.angleMode = event.target.value;
+      render();
+    });
+
+    addButtons(document.getElementById('stackButtons'), groups.stack);
+    addButtons(document.getElementById('arithButtons'), groups.arithmetic);
+    addButtons(document.getElementById('trigButtons'), groups.trig);
+    addButtons(document.getElementById('constButtons'), groups.const);
+
+    render();
+    focusScreen();
+  </script>
+</body>
+</html>
\ No newline at end of file
