Embed this calculator on your site
Free to use on any article or page. Pick a size, copy the code, and paste it in. It carries its own attribution and disclaimer, so there's nothing else to add.
1. Pick a size
Live preview, ~500px wide
2. Add the calculator
Paste this where you want the calculator to appear.
3. Add the resize script once
Paste this anywhere on the same page, once. It lets the calculator tell the iframe how tall to be, so there's no scrollbar or wasted space.