<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; font-family: system-ui, -apple-system, sans-serif; }
    body {
      background: #ffffff;
      color: #1e2945;
      width: 100%;
      min-height: 100%;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      padding: 12px 16px;
      user-select: none;
    }

    .toolbar {
      width: 100%;
      max-width: 680px;
      display: flex;
      justify-content: space-between;
      align-items: center;
      margin-bottom: 8px;
    }

    .btn-group {
      display: flex;
      gap: 8px;
    }

    button {
      background: #f8fafc;
      border: 1px solid #cbd5e1;
      color: #1e2945;
      padding: 6px 14px;
      border-radius: 6px;
      font-size: 14px;
      font-weight: 600;
      cursor: pointer;
      display: flex;
      align-items: center;
      gap: 6px;
    }
    button:active { background: #e2e8f0; }

    .timer-badge {
      font-variant-numeric: tabular-nums;
      font-weight: 700;
      font-size: 15px;
      color: #1e2945;
      background: #f1f5f9;
      padding: 6px 12px;
      border-radius: 6px;
      border: 1px solid #e2e8f0;
    }

    .stage-container {
      width: 100%;
      max-width: 680px;
      position: relative;
    }

    svg {
      width: 100%;
      height: auto;
      display: block;
      overflow: visible;
    }

    .legend {
      width: 100%;
      max-width: 680px;
      display: flex;
      justify-content: center;
      gap: 20px;
      margin-top: 10px;
      font-size: 13px;
      font-weight: 600;
    }

    .legend-item {
      display: flex;
      align-items: center;
      gap: 6px;
    }

    .legend-dot {
      width: 12px;
      height: 12px;
      border-radius: 50%;
    }
  </style>
</head>
<body>

  <div class="toolbar">
    <div class="btn-group">
      <button id="playBtn">⏸ Pause</button>
      <button id="resetBtn">↺ Restart</button>
    </div>
    <div class="timer-badge">Flight Time: <span id="timerVal">0.0</span> µs</div>
  </div>

  <div class="stage-container">
    <svg viewBox="0 0 680 280">
      
      <rect x="10" y="40" width="120" height="190" fill="#f8fafc" stroke="#e2e8f0" stroke-width="1.5" rx="4"/>
      <rect x="130" y="40" width="100" height="190" fill="#f0f9ff" stroke="#bae6fd" stroke-width="1.5" rx="4"/>
      <rect x="230" y="40" width="340" height="190" fill="#f8fafc" stroke="#e2e8f0" stroke-width="1.5" rx="4"/>
      <rect x="570" y="40" width="90" height="190" fill="#f1f5f9" stroke="#cbd5e1" stroke-width="1.5" rx="4"/>

      
      <text x="70" y="28" fill="#1e2945" font-size="13" font-weight="700" text-anchor="middle">1. Ionize</text>
      <text x="180" y="28" fill="#1e2945" font-size="13" font-weight="700" text-anchor="middle">2. Accelerate</text>
      <text x="400" y="28" fill="#1e2945" font-size="13" font-weight="700" text-anchor="middle">3. Drift Tube (d)</text>
      <text x="615" y="28" fill="#1e2945" font-size="13" font-weight="700" text-anchor="middle">4. Detect</text>

      
      
      <rect x="55" y="46" width="30" height="14" fill="#64748b" rx="2"/>
      <text x="70" y="42" fill="#64748b" font-size="10" text-anchor="middle">e⁻ Beam</text>
      <line id="eBeam" x1="70" y1="60" x2="70" y2="135" stroke="#22b7ff" stroke-width="2" stroke-dasharray="3,3"/>

      
      <line x1="145" y1="55" x2="145" y2="215" stroke="#0ea5e9" stroke-width="4" stroke-linecap="round"/>
      <text x="145" y="228" fill="#0ea5e9" font-size="11" font-weight="700" text-anchor="middle">+</text>
      
      <line x1="215" y1="55" x2="215" y2="215" stroke="#64748b" stroke-width="4" stroke-linecap="round"/>
      <text x="215" y="228" fill="#64748b" font-size="11" font-weight="700" text-anchor="middle">−</text>

      
      <path d="M 160 135 L 200 135 M 194 130 L 200 135 L 194 140" fill="none" stroke="#38bdf8" stroke-width="1.5" stroke-linecap="round"/>

      
      <line x1="590" y1="55" x2="590" y2="215" stroke="#1e2945" stroke-width="5" stroke-linecap="round"/>
      
      
      <circle id="hit24" cx="590" cy="95" r="8" fill="#22b7ff" opacity="0"/>
      <circle id="hit25" cx="590" cy="135" r="8" fill="#06b6d4" opacity="0"/>
      <circle id="hit26" cx="590" cy="175" r="8" fill="#1e3a8a" opacity="0"/>

      
      <g id="sig24" opacity="0.3">
        <text x="610" y="99" fill="#22b7ff" font-size="11" font-weight="700">t₁: 2.2 µs</text>
      </g>
      <g id="sig25" opacity="0.3">
        <text x="610" y="139" fill="#06b6d4" font-size="11" font-weight="700">t₂: 3.1 µs</text>
      </g>
      <g id="sig26" opacity="0.3">
        <text x="610" y="179" fill="#1e3a8a" font-size="11" font-weight="700">t₃: 4.2 µs</text>
      </g>

      
      <line x1="20" y1="95" x2="585" y2="95" stroke="#f1f5f9" stroke-width="1"/>
      <line x1="20" y1="135" x2="585" y2="135" stroke="#f1f5f9" stroke-width="1"/>
      <line x1="20" y1="175" x2="585" y2="175" stroke="#f1f5f9" stroke-width="1"/>

      
      <g id="ion24" transform="translate(45, 95)">
        <circle cx="0" cy="0" r="13" fill="#22b7ff"/>
        <text cx="0" y="4" fill="#ffffff" font-size="10" font-weight="700" text-anchor="middle">²⁴Mg⁺</text>
      </g>

      
      <g id="ion25" transform="translate(45, 135)">
        <circle cx="0" cy="0" r="14" fill="#06b6d4"/>
        <text cx="0" y="4" fill="#ffffff" font-size="10" font-weight="700" text-anchor="middle">²⁵Mg⁺</text>
      </g>

      
      <g id="ion26" transform="translate(45, 175)">
        <circle cx="0" cy="0" r="15" fill="#1e3a8a"/>
        <text cx="0" y="4" fill="#ffffff" font-size="10" font-weight="700" text-anchor="middle">²⁶Mg⁺</text>
      </g>

      
      <line x1="230" y1="248" x2="570" y2="248" stroke="#94a3b8" stroke-width="1.5" stroke-linecap="round"/>
      <line x1="230" y1="243" x2="230" y2="253" stroke="#94a3b8" stroke-width="1.5"/>
      <line x1="570" y1="243" x2="570" y2="253" stroke="#94a3b8" stroke-width="1.5"/>
      <text x="400" y="265" fill="#64748b" font-size="11" text-anchor="middle">Equal Kinetic Energy → Lower Mass Travels Faster</text>
    </svg>
  </div>

  <div class="legend">
    <div class="legend-item"><div class="legend-dot" style="background:#22b7ff"></div>²⁴Mg (Lightest · Fastest)</div>
    <div class="legend-item"><div class="legend-dot" style="background:#06b6d4"></div>²⁵Mg</div>
    <div class="legend-item"><div class="legend-dot" style="background:#1e3a8a"></div>²⁶Mg (Heaviest · Slowest)</div>
  </div>

  <script>
    const playBtn = document.getElementById('playBtn');
    const resetBtn = document.getElementById('resetBtn');
    const timerVal = document.getElementById('timerVal');
    
    const ion24 = document.getElementById('ion24');
    const ion25 = document.getElementById('ion25');
    const ion26 = document.getElementById('ion26');
    
    const hit24 = document.getElementById('hit24');
    const hit25 = document.getElementById('hit25');
    const hit26 = document.getElementById('hit26');
    
    const sig24 = document.getElementById('sig24');
    const sig25 = document.getElementById('sig25');
    const sig26 = document.getElementById('sig26');
    const eBeam = document.getElementById('eBeam');

    let isPlaying = true;
    let progress = 0; // 0 to 5.5s cycle
    const duration = 5.6;
    let lastTime = null;

    // Physical path coordinates
    const startX = 45;
    const accelStartX = 145;
    const driftStartX = 215;
    const detectX = 590;

    function getXPos(t, tArrival) {
      // Stage 1: Wait in ionization chamber (0.0 to 0.7s)
      if (t < 0.7) {
        return startX + (t / 0.7) * (accelStartX - startX);
      }
      // Stage 2: Acceleration (0.7 to 1.3s)
      if (t < 1.3) {
        const u = (t - 0.7) / 0.6;
        return accelStartX + (driftStartX - accelStartX) * (u * u);
      }
      // Stage 3: Drift Tube to Detector
      if (t < tArrival) {
        const u = (t - 1.3) / (tArrival - 1.3);
        return driftStartX + (detectX - driftStartX) * u;
      }
      // Reached detector
      return detectX;
    }

    function render(time) {
      // Electron beam flash during ionization phase
      eBeam.setAttribute('stroke-opacity', (progress < 0.7) ? (0.4 + 0.6 * Math.sin(progress * 20)) : '0.1');

      // Ion positions
      const x24 = getXPos(progress, 2.2);
      const x25 = getXPos(progress, 3.1);
      const x26 = getXPos(progress, 4.2);

      ion24.setAttribute('transform', `translate(${x24}, 95)`);
      ion25.setAttribute('transform', `translate(${x25}, 135)`);
      ion26.setAttribute('transform', `translate(${x26}, 175)`);

      // Detector hits & Signals
      const hit24Active = progress >= 2.2 && progress < 5.2;
      const hit25Active = progress >= 3.1 && progress < 5.2;
      const hit26Active = progress >= 4.2 && progress < 5.2;

      hit24.setAttribute('opacity', hit24Active ? '0.8' : '0');
      hit25.setAttribute('opacity', hit25Active ? '0.8' : '0');
      hit26.setAttribute('opacity', hit26Active ? '0.8' : '0');

      sig24.setAttribute('opacity', hit24Active ? '1' : '0.2');
      sig25.setAttribute('opacity', hit25Active ? '1' : '0.2');
      sig26.setAttribute('opacity', hit26Active ? '1' : '0.2');

      // Timer update
      const displayTime = Math.min(progress, 4.2).toFixed(1);
      timerVal.textContent = displayTime;
    }

    function tick(timestamp) {
      if (!lastTime) lastTime = timestamp;
      const dt = (timestamp - lastTime) / 1000;
      lastTime = timestamp;

      if (isPlaying) {
        progress += dt;
        if (progress > duration) {
          progress = 0; // loop seamlessly
        }
        render(progress);
      }
      requestAnimationFrame(tick);
    }

    playBtn.addEventListener('click', () => {
      isPlaying = !isPlaying;
      playBtn.textContent = isPlaying ? '⏸ Pause' : '▶ Play';
    });

    resetBtn.addEventListener('click', () => {
      progress = 0;
      render(progress);
      if (!isPlaying) {
        isPlaying = true;
        playBtn.textContent = '⏸ Pause';
      }
    });

    requestAnimationFrame(tick);
  </script>
</body>
</html>

Average Atomic Mass and Isotopic Abundance

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #ffffff;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      padding: 12px 16px;
      height: 100%;
      user-select: none;
    }
    .header {
      display: flex;
      align-items: center;
      justify-content: space-between;
      width: 100%;
      max-width: 580px;
      min-height: 28px;
    }
    .badge {
      font-size: 13px;
      font-weight: 600;
      color: #0284c7;
      background: #e0f2fe;
      border: 1px solid #bae6fd;
      padding: 3px 10px;
      border-radius: 999px;
      transition: all 0.2s ease;
      opacity: 0;
      transform: translateY(2px);
    }
    .badge.visible {
      opacity: 1;
      transform: translateY(0);
    }
    .title {
      font-size: 14px;
      font-weight: 700;
      color: #1e2945;
    }
    .chart-container {
      width: 100%;
      max-width: 580px;
      position: relative;
      flex: 1;
      display: flex;
      align-items: center;
    }
    svg {
      width: 100%;
      height: auto;
      overflow: visible;
    }
    .axis-line { stroke: #94a3b8; stroke-width: 1.5; stroke-linecap: square; }
    .grid-line { stroke: #f1f5f9; stroke-width: 1; stroke-dasharray: 2 2; }
    .axis-text { font-size: 11px; fill: #64748b; font-variant-numeric: tabular-nums; }
    .axis-label { font-size: 11px; fill: #475569; font-weight: 600; }
    
    .peak-line {
      stroke: #0284c7;
      stroke-width: 4;
      stroke-linecap: round;
      transition: stroke 0.2s ease, y1 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    }
    .peak-line.active {
      stroke: #22b7ff;
      stroke-width: 5;
    }
    .peak-dot {
      fill: #0284c7;
      transition: fill 0.2s ease, cy 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    }
    .peak-dot.active {
      fill: #22b7ff;
    }
    .hit-area {
      fill: transparent;
      cursor: pointer;
    }
    .toggle-bar {
      display: flex;
      background: #f1f5f9;
      padding: 3px;
      border-radius: 8px;
      gap: 4px;
      margin-top: 4px;
    }
    .toggle-btn {
      border: none;
      background: transparent;
      padding: 6px 14px;
      font-size: 12px;
      font-weight: 600;
      color: #64748b;
      border-radius: 6px;
      cursor: pointer;
      transition: all 0.2s ease;
    }
    .toggle-btn.active {
      background: #ffffff;
      color: #0284c7;
      box-shadow: 0 1px 3px rgba(0,0,0,0.1);
    }
  </style>
</head>
<body>
  <div class="header">
    <div class="title">Magnesium Mass Spectrum</div>
    <div id="badge" class="badge">Hover peak</div>
  </div>

  <div class="chart-container">
    <svg viewBox="0 0 540 240" id="spectrum">
      
      <g id="yGrid">
        <line x1="45" y1="20" x2="520" y2="20" class="grid-line" />
        <line x1="45" y1="60" x2="520" y2="60" class="grid-line" />
        <line x1="45" y1="100" x2="520" y2="100" class="grid-line" />
        <line x1="45" y1="140" x2="520" y2="140" class="grid-line" />
        <line x1="45" y1="180" x2="520" y2="180" class="grid-line" />

        <text x="38" y="24" text-anchor="end" class="axis-text" id="yLabel100">100</text>
        <text x="38" y="64" text-anchor="end" class="axis-text" id="yLabel80">80</text>
        <text x="38" y="104" text-anchor="end" class="axis-text" id="yLabel60">60</text>
        <text x="38" y="144" text-anchor="end" class="axis-text" id="yLabel40">40</text>
        <text x="38" y="184" text-anchor="end" class="axis-text" id="yLabel20">20</text>
        <text x="38" y="204" text-anchor="end" class="axis-text">0</text>
      </g>

      
      <line x1="45" y1="20" x2="45" y2="200" class="axis-line" />
      <line x1="45" y1="200" x2="520" y2="200" class="axis-line" />

      
      
      
      <g class="axis-text">
        <line x1="45" y1="200" x2="45" y2="205" class="axis-line" /><text x="45" y="218" text-anchor="middle">20</text>
        <line x1="92" y1="200" x2="92" y2="205" class="axis-line" /><text x="92" y="218" text-anchor="middle">21</text>
        <line x1="139" y1="200" x2="139" y2="205" class="axis-line" /><text x="139" y="218" text-anchor="middle">22</text>
        <line x1="186" y1="200" x2="186" y2="205" class="axis-line" /><text x="186" y="218" text-anchor="middle">23</text>
        <line x1="233" y1="200" x2="233" y2="205" class="axis-line" /><text x="233" y="218" text-anchor="middle" font-weight="bold" fill="#1e2945">24</text>
        <line x1="280" y1="200" x2="280" y2="205" class="axis-line" /><text x="280" y="218" text-anchor="middle" font-weight="bold" fill="#1e2945">25</text>
        <line x1="327" y1="200" x2="327" y2="205" class="axis-line" /><text x="327" y="218" text-anchor="middle" font-weight="bold" fill="#1e2945">26</text>
        <line x1="374" y1="200" x2="374" y2="205" class="axis-line" /><text x="374" y="218" text-anchor="middle">27</text>
        <line x1="421" y1="200" x2="421" y2="205" class="axis-line" /><text x="421" y="218" text-anchor="middle">28</text>
        <line x1="468" y1="200" x2="468" y2="205" class="axis-line" /><text x="468" y="218" text-anchor="middle">29</text>
        <line x1="515" y1="200" x2="515" y2="205" class="axis-line" /><text x="515" y="218" text-anchor="middle">30</text>
      </g>

      
      <text x="280" y="235" text-anchor="middle" class="axis-label">m/z (Mass-to-Charge Ratio)</text>
      <text x="-110" y="14" transform="rotate(-90)" text-anchor="middle" class="axis-label" id="yAxisTitle">Abundance (%)</text>

      
      
      <line id="peak24" x1="233" y1="57.8" x2="233" y2="200" class="peak-line" />
      <circle id="dot24" cx="233" cy="57.8" r="3.5" class="peak-dot" />

      
      <line id="peak25" x1="280" y1="182" x2="280" y2="200" class="peak-line" />
      <circle id="dot25" cx="280" cy="182" r="3.5" class="peak-dot" />

      
      <line id="peak26" x1="327" y1="180.2" x2="327" y2="200" class="peak-line" />
      <circle id="dot26" cx="327" cy="180.2" r="3.5" class="peak-dot" />

      
      <rect x="213" y="10" width="40" height="190" class="hit-area" data-iso="²⁴Mg" data-pct="78.99%" data-ratio="78.99" data-idx="24" />
      <rect x="260" y="10" width="40" height="190" class="hit-area" data-iso="²⁵Mg" data-pct="10.00%" data-ratio="10.00" data-idx="25" />
      <rect x="307" y="10" width="40" height="190" class="hit-area" data-iso="²⁶Mg" data-pct="11.01%" data-ratio="11.01" data-idx="26" />
    </svg>
  </div>

  <div class="toggle-bar">
    <button class="toggle-btn active" id="btnPct">Percentage Mode (100%)</button>
    <button class="toggle-btn" id="btnRatio">Peak Ratio Mode</button>
  </div>

  <script>
    const badge = document.getElementById('badge');
    const yAxisTitle = document.getElementById('yAxisTitle');
    const hitAreas = document.querySelectorAll('.hit-area');
    const btnPct = document.getElementById('btnPct');
    const btnRatio = document.getElementById('btnRatio');

    let mode = 'pct'; // 'pct' | 'ratio'
    let activePeak = null;

    const data = {
      24: { iso: '²⁴Mg', pct: '78.99%', ratio: '78.99', pctY: 57.8, ratioY: 57.8 },
      25: { iso: '²⁵Mg', pct: '10.00%', ratio: '10.00', pctY: 182.0, ratioY: 182.0 },
      26: { iso: '²⁶Mg', pct: '11.01%', ratio: '11.01', pctY: 180.2, ratioY: 180.2 }
    };

    function highlight(idx) {
      activePeak = idx;
      [24, 25, 26].forEach(i => {
        const peak = document.getElementById('peak' + i);
        const dot = document.getElementById('dot' + i);
        if (i === idx) {
          peak.classList.add('active');
          dot.classList.add('active');
        } else {
          peak.classList.remove('active');
          dot.classList.remove('active');
        }
      });

      if (idx) {
        const d = data[idx];
        const val = mode === 'pct' ? d.pct + ' abundance' : 'Ratio: ' + d.ratio;
        badge.textContent = `${d.iso}: ${val}`;
        badge.classList.add('visible');
      } else {
        badge.classList.remove('visible');
      }
    }

    hitAreas.forEach(area => {
      const idx = parseInt(area.getAttribute('data-idx'), 10);
      area.addEventListener('mouseenter', () => highlight(idx));
      area.addEventListener('mouseleave', () => highlight(null));
      area.addEventListener('touchstart', (e) => {
        e.preventDefault();
        highlight(idx);
      });
    });

    btnPct.addEventListener('click', () => {
      mode = 'pct';
      btnPct.classList.add('active');
      btnRatio.classList.remove('active');
      yAxisTitle.textContent = 'Abundance (%)';
      if (activePeak) highlight(activePeak);
    });

    btnRatio.addEventListener('click', () => {
      mode = 'ratio';
      btnRatio.classList.add('active');
      btnPct.classList.remove('active');
      yAxisTitle.textContent = 'Relative Peak Ratio';
      if (activePeak) highlight(activePeak);
    });

    // Default hover hint on 24
    setTimeout(() => {
      if (!activePeak) {
        highlight(24);
        setTimeout(() => { if (activePeak === 24) highlight(null); }, 1800);
      }
    }, 400);
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Relative Atomic Mass Calculation (Mg)</title>
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
      color: #1e2945;
      background: transparent;
      padding: 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100vh;
      box-sizing: border-box;
    }

    /* Stepper Header */
    .controls {
      display: flex;
      flex-wrap: wrap;
      align-items: center;
      justify-content: center;
      gap: 6px;
      width: 100%;
      max-width: 480px;
      margin-bottom: 8px;
    }
    .btn-step {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      border-radius: 6px;
      padding: 6px 10px;
      font-size: 12px;
      font-weight: 600;
      color: #475569;
      cursor: pointer;
      transition: background 0.2s ease, border-color 0.2s ease, box-shadow 0.2s ease;
    }
    .btn-step:hover {
      background: #e2e8f0;
    }
    .btn-step.active {
      background: #22b7ff;
      color: #ffffff;
      border-color: #0ea5e9;
      box-shadow: 0 0 8px rgba(34, 183, 255, 0.4);
    }

    /* Main Display Area without Card Container */
    .stage-container {
      width: 100%;
      max-width: 480px;
      flex: 1;
      display: flex;
      flex-direction: column;
      justify-content: center;
      align-items: center;
      padding: 12px 0;
    }

    /* Table (Step 1) */
    .table-wrapper {
      width: 100%;
      overflow-x: auto;
    }
    .data-table {
      width: 100%;
      border-collapse: collapse;
      text-align: center;
      font-size: 14px;
    }
    .data-table th {
      background: #f8fafc;
      padding: 8px 10px;
      border-bottom: 2px solid #cbd5e1;
      color: #475569;
      font-weight: 600;
    }
    .data-table td {
      padding: 9px 10px;
      border-bottom: 1px solid #e2e8f0;
      font-weight: 500;
    }
    .is-mg24 { color: #0284c7; font-weight: 600; }
    .is-mg25 { color: #0d9488; font-weight: 600; }
    .is-mg26 { color: #7c3aed; font-weight: 600; }

    /* Math Breakdown (Steps 2-4) */
    .calc-container {
      display: flex;
      flex-direction: column;
      gap: 14px;
      align-items: center;
      width: 100%;
    }

    .formula-line {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      font-size: clamp(13px, 3.8vw, 15px);
      font-weight: 600;
      width: 100%;
      text-align: center;
      flex-wrap: wrap;
    }

    .fraction {
      display: inline-flex;
      flex-direction: column;
      align-items: center;
      vertical-align: middle;
    }
    .numerator {
      border-bottom: 2px solid #1e2945;
      padding-bottom: 4px;
      margin-bottom: 4px;
      display: flex;
      gap: 4px;
      flex-wrap: wrap;
      justify-content: center;
      border-radius: 6px;
      padding: 4px 8px;
    }
    .denominator {
      padding-top: 2px;
      display: flex;
      gap: 4px;
      justify-content: center;
      border-radius: 6px;
      padding: 4px 8px;
    }

    .pulse-highlight {
      background: #e0f2fe !important;
      border: 1px solid #22b7ff !important;
      box-shadow: 0 0 8px rgba(34, 183, 255, 0.45);
    }

    .sub-result {
      font-size: clamp(12px, 3.4vw, 14px);
      color: #64748b;
      display: flex;
      gap: 6px;
      align-items: center;
      justify-content: center;
      flex-wrap: wrap;
      border-radius: 6px;
    }

    .final-badge {
      font-size: 20px;
      font-weight: 700;
      color: #0284c7;
      background: #e0f2fe;
      padding: 8px 20px;
      border-radius: 8px;
      border: 2px solid #22b7ff;
      margin-top: 6px;
      box-shadow: 0 0 10px rgba(34, 183, 255, 0.3);
    }

    /* Step Visibility */
    .step-view {
      display: none;
      width: 100%;
    }
    .step-view.active {
      display: flex;
      flex-direction: column;
      align-items: center;
      animation: fadeIn 0.25s ease;
    }

    @keyframes fadeIn {
      from { opacity: 0; transform: translateY(3px); }
      to { opacity: 1; transform: translateY(0); }
    }

    .nav-bar {
      display: flex;
      gap: 8px;
      margin-top: 8px;
      width: 100%;
      max-width: 480px;
      justify-content: space-between;
    }
    .btn-nav {
      flex: 1;
      padding: 8px 14px;
      background: #22b7ff;
      color: #fff;
      border: none;
      border-radius: 6px;
      font-size: 13px;
      font-weight: 600;
      cursor: pointer;
      text-align: center;
      transition: background 0.2s ease, opacity 0.2s ease;
    }
    .btn-nav:hover:not(:disabled) {
      background: #0ea5e9;
    }
    .btn-nav:disabled {
      background: #cbd5e1;
      cursor: not-allowed;
      opacity: 0.7;
    }
  </style>
</head>
<body>

  
  <div class="controls">
    <button class="btn-step active" onclick="setStep(0)">1. Data</button>
    <button class="btn-step" onclick="setStep(1)">2. Numerator</button>
    <button class="btn-step" onclick="setStep(2)">3. Denominator</button>
    <button class="btn-step" onclick="setStep(3)">4. Result</button>
  </div>

  
  <div class="stage-container">
    
    <div id="view-0" class="step-view active">
      <div class="table-wrapper">
        <table class="data-table">
          <thead>
            <tr>
              <th>Isotope</th>
              <th>Mass (m/z)</th>
              <th>Abundance</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td class="is-mg24"><sup>24</sup>Mg</td>
              <td><strong>24</strong></td>
              <td>78.99%</td>
            </tr>
            <tr>
              <td class="is-mg25"><sup>25</sup>Mg</td>
              <td><strong>25</strong></td>
              <td>10.00%</td>
            </tr>
            <tr>
              <td class="is-mg26"><sup>26</sup>Mg</td>
              <td><strong>26</strong></td>
              <td>11.01%</td>
            </tr>
          </tbody>
        </table>
      </div>
    </div>

    
    <div id="view-1" class="step-view">
      <div class="calc-container">
        <div class="formula-line">
          <div class="fraction">
            <div class="numerator pulse-highlight">
              <span class="is-mg24">(24 × 78.99)</span>&nbsp;+&nbsp;
              <span class="is-mg25">(25 × 10.00)</span>&nbsp;+&nbsp;
              <span class="is-mg26">(26 × 11.01)</span>
            </div>
            <div class="denominator">Σ Abundances</div>
          </div>
        </div>
        <div class="sub-result">
          = <span class="is-mg24">1895.76</span> + <span class="is-mg25">250.00</span> + <span class="is-mg26">286.26</span>
        </div>
        <div class="sub-result pulse-highlight" style="padding: 5px 12px; font-weight: 700; color: #1e2945;">
          Numerator = 2432.02
        </div>
      </div>
    </div>

    
    <div id="view-2" class="step-view">
      <div class="calc-container">
        <div class="formula-line">
          <div class="fraction">
            <div class="numerator">2432.02</div>
            <div class="denominator pulse-highlight">
              <span class="is-mg24">78.99</span> + 
              <span class="is-mg25">10.00</span> + 
              <span class="is-mg26">11.01</span>
            </div>
          </div>
        </div>
        <div class="sub-result pulse-highlight" style="padding: 5px 12px; font-weight: 700; color: #1e2945;">
          Denominator = 100.00
        </div>
      </div>
    </div>

    
    <div id="view-3" class="step-view">
      <div class="calc-container">
        <div class="formula-line">
          <span style="color: #64748b;">A<sub>r</sub>(Mg) =</span>
          <div class="fraction">
            <div class="numerator">2432.02</div>
            <div class="denominator">100.00</div>
          </div>
        </div>
        <div class="final-badge pulse-highlight">
          A<sub>r</sub> = 24.32
        </div>
      </div>
    </div>
  </div>

  
  <div class="nav-bar">
    <button id="prevBtn" class="btn-nav" style="background:#64748b;" onclick="prevStep()" disabled>← Back</button>
    <button id="nextBtn" class="btn-nav" onclick="nextStep()">Next Step →</button>
  </div>

  <script>
    let currentStep = 0;
    const totalSteps = 4;

    function setStep(step) {
      currentStep = step;
      
      // Update Step Tabs
      document.querySelectorAll('.btn-step').forEach((btn, idx) => {
        btn.classList.toggle('active', idx === step);
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        view.classList.toggle('active', idx === step);
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      const nextBtn = document.getElementById('nextBtn');
      if (step === totalSteps - 1) {
        nextBtn.textContent = 'Restart ↺';
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        nextBtn.textContent = 'Next Step →';
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    function prevStep() {
      if (currentStep > 0) {
        setStep(currentStep - 1);
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  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      color: #1e2945;
      background: #ffffff;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      padding: 16px;
      min-height: 100%;
      user-select: none;
    }

    .toggle-bar {
      display: flex;
      background: #f1f5f9;
      padding: 4px;
      border-radius: 24px;
      gap: 4px;
      max-width: 100%;
    }

    .toggle-btn {
      border: none;
      background: transparent;
      padding: 8px 16px;
      font-size: 13px;
      font-weight: 600;
      color: #64748b;
      border-radius: 20px;
      cursor: pointer;
      transition: all 0.25s ease;
      white-space: nowrap;
    }

    .toggle-btn.active {
      background: #ffffff;
      color: #0284c7;
      box-shadow: 0 2px 6px rgba(0,0,0,0.08);
    }

    .scale-svg {
      width: 100%;
      max-width: 540px;
      height: auto;
      overflow: visible;
    }

    .pivot-group, .atom-extra, .pivot-label, .ruler-indicator {
      transition: all 0.4s cubic-bezier(0.34, 1.2, 0.64, 1);
    }

    .atom {
      transition: transform 0.4s cubic-bezier(0.34, 1.2, 0.64, 1), opacity 0.3s ease;
    }
  </style>
</head>
<body>

  <div class="toggle-bar">
    <button id="btnSimple" class="toggle-btn" onclick="setMode('simple')">Simple Average (50 / 50)</button>
    <button id="btnWeighted" class="toggle-btn active" onclick="setMode('weighted')">Weighted Average (76% / 24%)</button>
  </div>

  <svg class="scale-svg" viewBox="0 0 540 280">
    <defs>
      
      <filter id="atomShadow" x="-20%" y="-20%" width="140%" height="140%">
        <feDropShadow dx="0" dy="3" stdDeviation="3" flood-opacity="0.15" />
      </filter>
      
      <radialGradient id="grad35" cx="35%" cy="35%" r="65%">
        <stop offset="0%" stop-color="#38bdf8" />
        <stop offset="100%" stop-color="#0284c7" />
      </radialGradient>
      
      <radialGradient id="grad37" cx="35%" cy="35%" r="65%">
        <stop offset="0%" stop-color="#818cf8" />
        <stop offset="100%" stop-color="#4f46e5" />
      </radialGradient>
    </defs>

    
    <g transform="translate(0, 50)">
      <line x1="100" y1="0" x2="440" y2="0" stroke="#cbd5e1" stroke-width="2" stroke-dasharray="4 4" />
      
      
      <line x1="100" y1="-6" x2="100" y2="6" stroke="#94a3b8" stroke-width="2" />
      <text x="100" y="-12" text-anchor="middle" font-size="12" font-weight="600" fill="#64748b">35.0</text>
      
      
      <line x1="270" y1="-6" x2="270" y2="6" stroke="#94a3b8" stroke-width="2" />
      <text x="270" y="-12" text-anchor="middle" font-size="12" font-weight="600" fill="#64748b">36.0</text>
      
      
      <line x1="440" y1="-6" x2="440" y2="6" stroke="#94a3b8" stroke-width="2" />
      <text x="440" y="-12" text-anchor="middle" font-size="12" font-weight="600" fill="#64748b">37.0</text>
    </g>

    
    <g id="groupLeft" transform="translate(100, 160)">
      
      <path d="M -45,0 L 45,0 L 35,6 L -35,6 Z" fill="#94a3b8" />

      
      <circle cx="0" cy="-24" r="22" fill="url(#grad35)" filter="url(#atomShadow)" />
      <text x="0" y="-19" text-anchor="middle" fill="#ffffff" font-size="13" font-weight="700">³⁵Cl</text>

      
      <g id="extraAtoms" style="opacity: 1; transform: scale(1);">
        <circle cx="-22" cy="-64" r="22" fill="url(#grad35)" filter="url(#atomShadow)" />
        <text x="-22" y="-59" text-anchor="middle" fill="#ffffff" font-size="13" font-weight="700">³⁵Cl</text>

        <circle cx="22" cy="-64" r="22" fill="url(#grad35)" filter="url(#atomShadow)" />
        <text x="22" y="-59" text-anchor="middle" fill="#ffffff" font-size="13" font-weight="700">³⁵Cl</text>
      </g>

      
      <text id="labelLeft" x="0" y="32" text-anchor="middle" font-size="13" font-weight="700" fill="#0284c7">76%</text>
    </g>

    
    <g id="groupRight" transform="translate(440, 160)">
      
      <path d="M -45,0 L 45,0 L 35,6 L -35,6 Z" fill="#94a3b8" />

      
      <circle cx="0" cy="-24" r="22" fill="url(#grad37)" filter="url(#atomShadow)" />
      <text x="0" y="-19" text-anchor="middle" fill="#ffffff" font-size="13" font-weight="700">³⁷Cl</text>

      
      <text id="labelRight" x="0" y="32" text-anchor="middle" font-size="13" font-weight="700" fill="#4f46e5">24%</text>
    </g>

    
    <rect x="70" y="160" width="400" height="8" rx="4" fill="#334155" />

    
    
    
    <g id="pivotGroup" class="pivot-group" transform="translate(181.6, 168)">
      
      <polygon points="0,0 -18,36 18,36" fill="#0284c7" />
      <circle cx="0" cy="0" r="4" fill="#ffffff" />
      
      
      <rect x="-30" y="36" width="60" height="6" rx="3" fill="#64748b" />

      
      <path d="M 0,-8 L -6,-16 L 6,-16 Z" fill="#0284c7" />
      
      
      <g transform="translate(0, 68)">
        <rect x="-42" y="-14" width="84" height="26" rx="13" fill="#0284c7" />
        <text id="pivotVal" x="0" y="4" text-anchor="middle" fill="#ffffff" font-size="13" font-weight="700">35.48</text>
      </g>
    </g>
  </svg>

  <script>
    function setMode(mode) {
      const isWeighted = mode === 'weighted';
      
      // Update Buttons
      document.getElementById('btnSimple').classList.toggle('active', !isWeighted);
      document.getElementById('btnWeighted').classList.toggle('active', isWeighted);

      // Pivot position: 35.0 = 100px, 37.0 = 440px (170px per unit)
      // Weighted: 35.48 -> 100 + (0.48 * 170) = 181.6
      // Simple: 36.00 -> 100 + (1.00 * 170) = 270
      const pivotX = isWeighted ? 181.6 : 270;
      document.getElementById('pivotGroup').setAttribute('transform', `translate(${pivotX}, 168)`);
      document.getElementById('pivotVal').textContent = isWeighted ? '35.48' : '36.00';

      // Extra atoms on Cl-35 side
      const extra = document.getElementById('extraAtoms');
      extra.style.opacity = isWeighted ? '1' : '0';
      extra.style.transform = isWeighted ? 'scale(1)' : 'scale(0.3)';

      // Labels
      document.getElementById('labelLeft').textContent = isWeighted ? '76%' : '50%';
      document.getElementById('labelRight').textContent = isWeighted ? '24%' : '50%';
    }
  </script>
</body>
</html>

OGS.13.CH.2

Aligned learning resources

Related diagrams