Privacy

Effective October 8, 2026. Last updated October 8, 2026.

Our commitment

These lessons are for learning mathematics, and nothing else. Every course and lesson works without an account, and nothing you do here is sent to us. We will never sell, share or monetize anything about you.

What we collect

Nothing about you or your use of the lessons. The site has no accounts, no sign-in, and nothing on it sends anything back. Our server sends you the pages and the calculator, and keeps no record of the pages you visit.

We don't log the pages you visit. Our server's firewall and proxy keep IP addresses only from connections that fail or are blocked, for up to about four months (firewall) and until the proxy is next restarted from scratch (proxy errors).

Your browser keeps these for you, on your device only:

• your choice of calculator mode (33s, 35s or STU) and of entry (algebraic or RPN);
• the Try it speed you chose in Settings;
• your progress: which examples you have tried, which lessons you marked finished, and which questions you answered right (a wrong answer keeps nothing);
• the unit a placement check suggested, per course (your answers to it are kept nowhere).

They stay in your browser's storage for this site. They are never sent to us or to anyone else. Your achievements are worked out from your progress each time you look; nothing more is kept for them.

What we do not collect

• We do not use analytics, advertising pixels or any third-party tracking scripts.
• We do not use cookies at all.
• We do not build profiles of how anyone uses the site.

Your choices

• Forget your progress at any time in Settings.
• Save your progress to a file, and load it on another browser or device, also in Settings. The file is saved on your device and read in your browser: it is never sent to us, and holds only your progress (no name, no date).
• Clearing this site's data in your browser removes everything listed above.
• A private window keeps nothing after it closes.

Data sharing

We share nothing with anyone: we hold nothing about you beyond the failed-connection records above, which only keep the server safe.

Children's privacy

Some courses are written for learners as young as 12. The site asks no one for personal information, children included: no account, no name, no email, no age. If we ever add optional accounts, a learner under 13 will only be added by a parent or teacher, with a parent's consent, and this page will say so first.

Changes to this policy

If this policy changes, the "Last updated" date above changes with it, and a change that collects anything new will be described here before it happens.

Contact

Questions about this policy? Write to stuffleberryco+privacy@gmail.com.