For grown-ups
InventForge is struggle before instruction. The pair looks at three machines' throws with no formula, invents a measure of spread from simple parts, and tests it on new cases.
Only then does the standard deviation arrive, and the app shows where the invented measure and the textbook disagree. The textbook's choice is a convention; other measures of spread serve too, and the app says so.
Nothing is stored or sent.
What it never does
- No accounts, no ads, no tracking — anything kept stays on this device.
- No streaks, timers to beat, points to chase or leaderboards.
- No chat, and nothing anyone types is sent anywhere.