<label for="expr">Enter expression (a‑b‑c):</label><br> <input id="expr" type="text" placeholder="e.g. 5-1-1.5" size="20"> <button id="validateBtn">Validate</button>
<script> const TOLERANCE = 0.001; // allow tiny floating‑point drift const TARGET = 2.5; // metres const downloadBtn = document.querySelector('#downloadBtn button'); const msg = document.getElementById('msg'); x-x-x is equal to 2 5 meter download link
document.getElementById('validateBtn').addEventListener('click', validate); // optional live validation: // document.getElementById('expr').addEventListener('input', validate); </script> </body> </html> If you need to generate the file on the fly (e.g., a PDF ruler with custom branding), a simple endpoint could be: | | Static CDN | Store the file once ( 2_5m_ruler
| Tech | Example | |------|---------| | | GET /download?length=2.5 → uses pdfkit to render a 2.5 m ruler PDF, streams it back. | | Python/Flask | @app.route('/download') → builds an SVG/PNG with cairosvg . | | Static CDN | Store the file once ( 2_5m_ruler.pdf ) and serve via CloudFront, Akamai, etc. | etc. | <
<p id="msg"></p>
function validate() const expr = document.getElementById('expr').value; const result = parseAndEval(expr); if (result === null) msg.textContent = 'Invalid format – use a‑b‑c (numbers only).'; msg.className = 'invalid'; downloadBtn.disabled = true; return; if (Math.abs(result - TARGET) <= TOLERANCE) msg.textContent = `Result: $result m ✅`; msg.className = 'valid'; downloadBtn.disabled = false; else msg.textContent = `Result: $result m – must equal $TARGET m.`; msg.className = 'invalid'; downloadBtn.disabled = true;