A good question builds things too.

Our email is [email protected]. We read every message, in English or Spanish.

What helps us

A calculation error: the tool's name, the values with their units, the result you got and the one you expected.
Something that looks wrong: which browser you use and whether it happened on a computer, tablet or phone. If you can, the steps to make it happen again.
Ideas: another tool, an experiment or a topic you'd like explained.
If you're a teacher: tell us what subject and level you teach; it helps us prepare tools and activities for class.

Don't include passwords or personal data that aren't needed. The tools don't save anything, so the values you used are all we need to help you.

What we do with your email is explained in the privacy notice.