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System default

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Tutoring abilities

Look closely at the tip of your pinky finger.

The width across your little fingernail is about one **centimeter**.

<!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: #f8f9fa;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      padding: 16px;
      min-height: 100%;
      user-select: none;
    }

    .display-area {
      width: 100%;
      max-width: 520px;
      background: #ffffff;
      border-radius: 12px;
      padding: 12px 8px;
      box-shadow: 0 2px 8px rgba(0, 0, 0, 0.05);
      display: flex;
      flex-direction: column;
      align-items: center;
    }

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

    .btn-group {
      display: flex;
      flex-wrap: wrap;
      gap: 8px;
      justify-content: center;
      width: 100%;
      max-width: 520px;
      margin-top: 12px;
    }

    .item-btn {
      background: #ffffff;
      border: 2px solid transparent;
      border-radius: 10px;
      padding: 8px 14px;
      font-size: 15px;
      font-weight: 600;
      color: #1e2945;
      cursor: pointer;
      display: flex;
      align-items: center;
      gap: 6px;
      box-shadow: 0 1px 4px rgba(0,0,0,0.06);
      transition: background 0.2s, border-color 0.2s, color 0.2s;
    }

    .item-btn:hover {
      background: #f1f5f9;
    }

    .item-btn.active {
      background: #e8f7ff;
      border-color: #22b7ff;
      color: #008ecc;
    }

    .measure-tag {
      font-size: 18px;
      font-weight: 800;
      fill: #008ecc;
      text-anchor: middle;
      transition: x 0.35s ease;
    }

    .guide-line {
      stroke: #22b7ff;
      stroke-width: 2;
      stroke-dasharray: 4 3;
      transition: all 0.35s ease;
    }

    .measure-span {
      stroke: #22b7ff;
      stroke-width: 3;
      stroke-linecap: round;
      transition: all 0.35s ease;
    }

    .obj-graphic {
      transition: opacity 0.25s ease, transform 0.35s ease;
      transform-origin: 50px 75px;
    }
  </style>
</head>
<body>

  <div class="display-area">
    <svg viewBox="0 0 500 210">
      <defs>
        
        <linearGradient id="rulerGrad" x1="0" y1="0" x2="0" y2="1">
          <stop offset="0%" stop-color="#fff8e7" />
          <stop offset="100%" stop-color="#faecc8" />
        </linearGradient>
      </defs>

      
      
      <g id="obj-0" class="obj-graphic">
        
        <path d="M 15 88 C 15 62, 75 62, 85 75 C 95 88, 90 98, 90 102 L 15 102 Z" fill="#ffd1b3" />
        <path d="M 50 68 C 50 64, 88 64, 88 78 C 88 88, 50 88, 50 68 Z" fill="#ffeae0" stroke="#f0baa0" stroke-width="1.5" />
      </g>

      
      <g id="obj-1" class="obj-graphic" style="opacity: 0; display: none;">
        <path d="M 60 84 L 180 84 C 192 84, 192 64, 180 64 L 70 64 C 54 64, 54 94, 70 94 L 175 94 C 185 94, 185 74, 175 74 L 80 74" 
              fill="none" stroke="#e056fd" stroke-width="6" stroke-linecap="round" stroke-linejoin="round" />
      </g>

      
      <g id="obj-2" class="obj-graphic" style="opacity: 0; display: none;">
        <rect x="50" y="60" width="200" height="34" rx="6" fill="#38ef7d" />
        <rect x="50" y="60" width="70" height="34" rx="6" fill="#11998e" opacity="0.4" />
        <line x1="120" y1="60" x2="120" y2="94" stroke="#ffffff" stroke-width="2" stroke-dasharray="3 3" />
      </g>

      
      <g id="obj-3" class="obj-graphic" style="opacity: 0; display: none;">
        <polygon points="50,77 75,64 75,90" fill="#ff4757" />
        <rect x="75" y="64" width="310" height="26" fill="#ff6b81" />
        <rect x="130" y="64" width="180" height="26" fill="#2f3542" />
        <rect x="140" y="68" width="160" height="18" fill="#57606f" rx="3" />
        <polygon points="385,64 400,77 385,90" fill="#ff4757" />
      </g>

      
      <line id="guide-left" class="guide-line" x1="50" y1="35" x2="50" y2="120" />
      <line id="guide-right" class="guide-line" x1="100" y1="35" x2="100" y2="120" />
      <line id="span-bar" class="measure-span" x1="50" y1="40" x2="100" y2="40" />
      <circle id="dot-left" cx="50" cy="40" r="4" fill="#22b7ff" />
      <circle id="dot-right" cx="100" cy="40" r="4" fill="#22b7ff" />
      <text id="measure-label" class="measure-tag" x="75" y="28">1 cm</text>

      
      <rect x="35" y="115" width="430" height="75" rx="6" fill="url(#rulerGrad)" stroke="#d9c18d" stroke-width="2" />

      
      <text x="440" y="172" font-size="14" font-weight="700" fill="#8c7647" text-anchor="end">cm</text>

      
      <g stroke="#6e5727" stroke-linecap="round" id="ruler-marks">
        
        
        <line x1="50" y1="115" x2="50" y2="148" stroke-width="2.5" />
        <text x="50" y="172" font-size="16" font-weight="700" fill="#4a3b19" text-anchor="middle">0</text>

        
        <line x1="100" y1="115" x2="100" y2="148" stroke-width="2.5" />
        <text x="100" y="172" font-size="16" font-weight="700" fill="#4a3b19" text-anchor="middle">1</text>

        
        <line x1="150" y1="115" x2="150" y2="148" stroke-width="2.5" />
        <text x="150" y="172" font-size="16" font-weight="700" fill="#4a3b19" text-anchor="middle">2</text>

        
        <line x1="200" y1="115" x2="200" y2="148" stroke-width="2.5" />
        <text x="200" y="172" font-size="16" font-weight="700" fill="#4a3b19" text-anchor="middle">3</text>

        
        <line x1="250" y1="115" x2="250" y2="148" stroke-width="2.5" />
        <text x="250" y="172" font-size="16" font-weight="700" fill="#4a3b19" text-anchor="middle">4</text>

        
        <line x1="300" y1="115" x2="300" y2="148" stroke-width="2.5" />
        <text x="300" y="172" font-size="16" font-weight="700" fill="#4a3b19" text-anchor="middle">5</text>

        
        <line x1="350" y1="115" x2="350" y2="148" stroke-width="2.5" />
        <text x="350" y="172" font-size="16" font-weight="700" fill="#4a3b19" text-anchor="middle">6</text>

        
        <line x1="400" y1="115" x2="400" y2="148" stroke-width="2.5" />
        <text x="400" y="172" font-size="16" font-weight="700" fill="#4a3b19" text-anchor="middle">7</text>

        
        <line x1="450" y1="115" x2="450" y2="148" stroke-width="2.5" />
        <text x="450" y="172" font-size="16" font-weight="700" fill="#4a3b19" text-anchor="middle">8</text>

        
        
        <g stroke-width="1.5">
          <line x1="75" y1="115" x2="75" y2="136" />
          <line x1="125" y1="115" x2="125" y2="136" />
          <line x1="175" y1="115" x2="175" y2="136" />
          <line x1="225" y1="115" x2="225" y2="136" />
          <line x1="275" y1="115" x2="275" y2="136" />
          <line x1="325" y1="115" x2="325" y2="136" />
          <line x1="375" y1="115" x2="375" y2="136" />
          <line x1="425" y1="115" x2="425" y2="136" />
        </g>
      </g>
    </svg>
  </div>

  
  <div class="btn-group">
    <button class="item-btn active" onclick="selectItem(0, 1)">💅 Fingernail</button>
    <button class="item-btn" onclick="selectItem(1, 3)">📎 Paperclip</button>
    <button class="item-btn" onclick="selectItem(2, 4)">🧼 Eraser</button>
    <button class="item-btn" onclick="selectItem(3, 7)">🖍️ Crayon</button>
  </div>

  <script>
    const items = [
      { cm: 1 },
      { cm: 3 },
      { cm: 4 },
      { cm: 7 }
    ];

    let currentIndex = 0;
    const startX = 50;
    const scale = 50; // 50px per 1 cm

    function selectItem(index, cm) {
      currentIndex = index;

      // Update buttons
      const buttons = document.querySelectorAll('.item-btn');
      buttons.forEach((btn, idx) => {
        btn.classList.toggle('active', idx === index);
      });

      // Update object visibility
      items.forEach((_, idx) => {
        const el = document.getElementById(`obj-${idx}`);
        if (idx === index) {
          el.style.display = 'block';
          setTimeout(() => { el.style.opacity = '1'; }, 10);
        } else {
          el.style.opacity = '0';
          setTimeout(() => { if (currentIndex !== idx) el.style.display = 'none'; }, 250);
        }
      });

      // Update measurement span & guides
      const endX = startX + (cm * scale);
      const midX = (startX + endX) / 2;

      const guideRight = document.getElementById('guide-right');
      const spanBar = document.getElementById('span-bar');
      const dotRight = document.getElementById('dot-right');
      const measureLabel = document.getElementById('measure-label');

      guideRight.setAttribute('x1', endX);
      guideRight.setAttribute('x2', endX);
      spanBar.setAttribute('x2', endX);
      dotRight.setAttribute('cx', endX);

      measureLabel.setAttribute('x', midX);
      measureLabel.textContent = `${cm} cm`;
    }
  </script>
</body>
</html>

How can we measure bigger things without lining up dozens of fingers?

A **ruler** is a straight measuring tool with numbers printed in order along the edge.

We often write **cm** as the short name for centimeter so it fits easily on the ruler.

<!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;
      user-select: none;
      -webkit-user-select: none;
    }

    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
      background: #f8f9fa;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
      padding: 12px;
    }

    .header-bar {
      display: flex;
      align-items: center;
      justify-content: space-between;
      width: 100%;
      max-width: 480px;
      margin-bottom: 4px;
    }

    .badge-unit {
      background: #e0f2fe;
      color: #0284c7;
      font-weight: 700;
      font-size: 14px;
      padding: 4px 10px;
      border-radius: 20px;
      border: 1px solid #bae6fd;
    }

    .total-display {
      font-size: 20px;
      font-weight: 800;
      color: #0284c7;
      display: flex;
      align-items: baseline;
      gap: 4px;
    }

    .total-display span {
      font-size: 14px;
      font-weight: 600;
      color: #64748b;
    }

    .stage {
      width: 100%;
      max-width: 480px;
      position: relative;
      display: flex;
      justify-content: center;
      align-items: center;
    }

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

    .arc-path {
      fill: none;
      stroke: #22b7ff;
      stroke-width: 3;
      stroke-linecap: round;
      stroke-dasharray: 200;
      stroke-dashoffset: 0;
      transition: opacity 0.3s ease, stroke-dashoffset 0.4s ease;
    }

    .arc-text {
      font-size: 13px;
      font-weight: 700;
      fill: #0284c7;
      text-anchor: middle;
      transition: opacity 0.3s ease;
    }

    .ruler-body {
      fill: #ffffff;
      stroke: #cbd5e1;
      stroke-width: 2;
      rx: 8;
    }

    .tick-major {
      stroke: #1e2945;
      stroke-width: 2;
      stroke-linecap: round;
    }

    .tick-mid {
      stroke: #64748b;
      stroke-width: 1.5;
      stroke-linecap: round;
    }

    .tick-minor {
      stroke: #94a3b8;
      stroke-width: 1;
      stroke-linecap: round;
    }

    .ruler-num {
      font-size: 16px;
      font-weight: 700;
      fill: #1e2945;
      text-anchor: middle;
    }

    .ruler-label {
      font-size: 12px;
      font-weight: 800;
      fill: #0284c7;
    }

    .highlight-span {
      fill: rgba(34, 183, 255, 0.15);
      transition: width 0.3s ease;
    }

    .controls {
      display: flex;
      gap: 6px;
      width: 100%;
      max-width: 480px;
      justify-content: center;
      flex-wrap: wrap;
      margin-top: 8px;
    }

    .btn {
      background: #ffffff;
      border: 2px solid #e2e8f0;
      color: #1e2945;
      font-size: 14px;
      font-weight: 700;
      padding: 8px 14px;
      border-radius: 10px;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      justify-content: center;
      transition: background-color 0.2s, border-color 0.2s, color 0.2s;
      min-height: 40px;
    }

    .btn.active {
      background: #22b7ff;
      border-color: #22b7ff;
      color: #ffffff;
      box-shadow: 0 2px 6px rgba(34, 183, 255, 0.35);
    }
  </style>
</head>
<body>

  <div class="header-bar">
    <div class="badge-unit">cm = centimeter</div>
    <div class="total-display" id="totalLabel">1 <span>cm</span></div>
  </div>

  <div class="stage">
    <svg viewBox="0 0 460 210" id="rulerSvg">
      <defs>
        <marker id="arrow" viewBox="0 0 10 10" refX="6" refY="5" markerWidth="6" markerHeight="6" orient="auto-start-reverse">
          <path d="M 0 1 L 8 5 L 0 9 z" fill="#22b7ff" />
        </marker>
      </defs>

      
      <rect id="highlightRect" class="highlight-span" x="40" y="110" width="76" height="70" rx="4" />

      
      <g id="arcsGroup"></g>

      
      <rect class="ruler-body" x="20" y="110" width="420" height="75" />

      
      <g id="ticksGroup"></g>
    </svg>
  </div>

  <div class="controls">
    <button class="btn active" data-val="1">1 cm</button>
    <button class="btn" data-val="2">2 cm</button>
    <button class="btn" data-val="3">3 cm</button>
    <button class="btn" data-val="4">4 cm</button>
    <button class="btn" data-val="5">5 cm</button>
  </div>

  <script>
    const startX = 40;
    const unitWidth = 76; // 1 cm = 76px
    const totalUnits = 5;
    const ticksGroup = document.getElementById('ticksGroup');
    const arcsGroup = document.getElementById('arcsGroup');
    const highlightRect = document.getElementById('highlightRect');
    const totalLabel = document.getElementById('totalLabel');
    const buttons = document.querySelectorAll('.btn');

    // Build Ruler Ticks
    for (let cm = 0; cm <= totalUnits; cm++) {
      const x = startX + (cm * unitWidth);

      // Major tick
      const majorLine = document.createElementNS('http://www.w3.org/2000/svg', 'line');
      majorLine.setAttribute('class', 'tick-major');
      majorLine.setAttribute('x1', x);
      majorLine.setAttribute('y1', 110);
      majorLine.setAttribute('x2', x);
      majorLine.setAttribute('y2', 138);
      ticksGroup.appendChild(majorLine);

      // Number
      const text = document.createElementNS('http://www.w3.org/2000/svg', 'text');
      text.setAttribute('class', 'ruler-num');
      text.setAttribute('x', x);
      text.setAttribute('y', 162);
      text.textContent = cm;
      ticksGroup.appendChild(text);

      // Sub-ticks
      if (cm < totalUnits) {
        for (let mm = 1; mm < 10; mm++) {
          const subX = x + (mm * (unitWidth / 10));
          const isMid = mm === 5;
          const subLine = document.createElementNS('http://www.w3.org/2000/svg', 'line');
          subLine.setAttribute('class', isMid ? 'tick-mid' : 'tick-minor');
          subLine.setAttribute('x1', subX);
          subLine.setAttribute('y1', 110);
          subLine.setAttribute('x2', subX);
          subLine.setAttribute('y2', isMid ? 128 : 120);
          ticksGroup.appendChild(subLine);
        }
      }
    }

    // "cm" label on the ruler
    const cmLabel = document.createElementNS('http://www.w3.org/2000/svg', 'text');
    cmLabel.setAttribute('class', 'ruler-label');
    cmLabel.setAttribute('x', startX + (totalUnits * unitWidth) + 8);
    cmLabel.setAttribute('y', 130);
    cmLabel.textContent = 'cm';
    ticksGroup.appendChild(cmLabel);

    // Update Jump Arcs
    function setMeasurement(count) {
      arcsGroup.innerHTML = '';
      highlightRect.setAttribute('width', count * unitWidth);
      totalLabel.innerHTML = `${count} <span>cm</span>`;

      for (let i = 0; i < count; i++) {
        const x1 = startX + (i * unitWidth);
        const x2 = startX + ((i + 1) * unitWidth);
        const midX = (x1 + x2) / 2;

        const path = document.createElementNS('http://www.w3.org/2000/svg', 'path');
        path.setAttribute('class', 'arc-path');
        path.setAttribute('d', `M ${x1 + 2} 102 Q ${midX} 45 ${x2 - 3} 102`);
        path.setAttribute('marker-end', 'url(#arrow)');
        arcsGroup.appendChild(path);

        const txt = document.createElementNS('http://www.w3.org/2000/svg', 'text');
        txt.setAttribute('class', 'arc-text');
        txt.setAttribute('x', midX);
        txt.setAttribute('y', 56);
        txt.textContent = '1 cm';
        arcsGroup.appendChild(txt);
      }
    }

    // Button interactions
    buttons.forEach(btn => {
      btn.addEventListener('click', () => {
        buttons.forEach(b => b.classList.remove('active'));
        btn.classList.add('active');
        setMeasurement(parseInt(btn.getAttribute('data-val'), 10));
      });
    });

    // Initialize with 1 cm
    setMeasurement(1);
  </script>
</body>
</html>

Each jump from one number to the next number is exactly 1 centimeter long.

What everyday objects in your classroom are about one centimeter wide?

A small shirt button, a sweet blueberry, and a plastic counting cube are all about 1 centimeter across.

<!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: #f8f9fa;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100vh;
      padding: 16px 12px;
      user-select: none;
    }

    /* Object Selector Tabs */
    .item-tabs {
      display: flex;
      flex-wrap: wrap;
      justify-content: center;
      gap: 8px;
      width: 100%;
      max-width: 460px;
    }
    .tab-btn {
      flex: 1 1 80px;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      background: #ffffff;
      border: 2px solid #e6e6e6;
      border-radius: 10px;
      padding: 8px 10px;
      font-size: 14px;
      font-weight: 600;
      color: #1e2945;
      cursor: pointer;
      box-shadow: 0 1px 3px rgba(0,0,0,0.04);
      transition: border-color 0.2s ease, background 0.2s ease, transform 0.1s ease;
    }
    .tab-btn.active {
      border-color: #22b7ff;
      background: #f0f9ff;
      color: #0284c7;
    }

    /* Main Visual Stage */
    .stage {
      position: relative;
      width: 100%;
      max-width: 480px;
      height: 240px;
      background: #ffffff;
      border-radius: 16px;
      box-shadow: 0 4px 12px rgba(0,0,0,0.05);
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: flex-end;
      padding-bottom: 24px;
      overflow: hidden;
    }

    /* Target Measurement Zone (0 to 1 cm) */
    .measure-zone {
      position: absolute;
      top: 20px;
      bottom: 74px;
      left: calc(10% + 2px);
      width: 16%;
      border-left: 2px dashed #22b7ff;
      border-right: 2px dashed #22b7ff;
      background: rgba(34, 183, 255, 0.08);
      border-radius: 4px;
      pointer-events: none;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: flex-start;
      padding-top: 8px;
    }
    .measure-badge {
      background: #22b7ff;
      color: #ffffff;
      font-size: 13px;
      font-weight: 700;
      padding: 3px 8px;
      border-radius: 6px;
      letter-spacing: 0.5px;
      box-shadow: 0 2px 4px rgba(34,183,255,0.3);
    }
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<body>

  
  <div class="item-tabs">
    <button class="tab-btn active" data-index="0">💅 Pinky</button>
    <button class="tab-btn" data-index="1">🔘 Button</button>
    <button class="tab-btn" data-index="2">🫐 Berry</button>
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        <span>▶</span>
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          <text x="360" y="44">4</text>
          <text x="440" y="44">5</text>
          <text x="475" y="32" font-size="11" font-weight="600" fill="#6b7280">cm</text>
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Whenever you see the letters **cm**, just picture your pinky fingernail to remember how big that space is!

math

Introducing the Centimeter and the Ruler. Identify the centimeter unit on a standard ruler and recognize about how wide 1 centimeter is.

How to Measure Length and Height Using Standard Units

Measuring Lengths (Centimeters and Meters) - Early Math

Measure Using a Centimetre Ruler

At Early Level (P1 / foundational primary), pedagogy must bridge non-standard concrete manipulatives (e.g., $1\text{ cm}$ unit cubes snapped together) to the continuous scale of a standard ruler. Begin by having learners physically place individual $1\text{ cm}$ cubes along a line, then overlay the ruler directly beneath the cube train to reveal that the ruler is simply a numbered track of standard centimetre units. Consistently reinforce bodily and everyday reference benchmarks (e.g., width of a finger, button, or paperclip) to cultivate intuitive estimation skills before formal measurement with instruments.

Introducing the Centimeter and the Ruler

Meet the Ruler

Things That Are 1 cm