Corrections
This page lists corrections to lessons that were already published: a wrong fact, a wrong answer to a question, a wrong value in a 3D scene, or a translation that changed the meaning. Small wording fixes are not listed one by one.
How to report a mistake
Every page has a Report a problem button near the bottom. It sends us the page address, the language and any sentence you have selected, so you only need to say what is wrong and what it should be. You can also use the contact form.
What happens to a report
- We open the lesson and check the sentence, the question or the scene against the sources listed for the course.
- If it is wrong, we fix it in English and Korean first and then in every language the lesson is published in.
- Corrections that change a fact or an answer are added to the table below.
Before a course is published, every unit also goes through a fact check against its sources; see how lessons are made.
Corrections
| Date | Lesson | What changed |
|---|---|---|
| 2026-10-21 | German and Japanese pages | A reader-order review of the home page, subject introductions, course titles and unit leads fixed 76 German and 71 Japanese wordings, including terms that had been translated with the wrong meaning. |
| 2026-10-19 | Geometry: triangles | The date given for Euclid was corrected to about 2,300 years ago (source: MacTutor History of Mathematics). |
| 2026-10-19 | Computer basics: typing (Korean) | On the Korean two-set (두벌식) keyboard, ㅠ is typed with the left hand. The lesson had it wrong. |
| 2026-10-19 | Geography: globe | Three bugs in the 3D globe quiz were fixed. |
| 2026-10-18 | Human body: heart, skeleton, brain | Lines that read as personal health advice were removed; the lessons explain how the body works and do not give medical advice. |
| 2026-10-18 | Music: ukulele strumming | The waltz strumming pattern did not fill all 4 bars. Corrected. |
| 2026-10-17 | Space: stars | The lifetime shown for red dwarf stars in the 3D scene was corrected to match the lesson's source. |