Learn Quaternions vs Understood In Spanish

Learning quaternions doesn't have to be hard! This app is a visual way to learn how quaternions work that makes it fun and interactive. Move the sliders to see the angle and axis of rotation change. Drag across screen to move around the scene. Made with RealityKit.

Understood In Spanish is a complete Spanish course, A1 to C2, with real grammar explanations, speaking practice and typed answers. Every lesson is free, and every explanation is in your own language. EVERY LESSON IS FREE • 280 lessons across 70 units, from complete beginner (A1) to C2 • No hearts, no energy bars, no lessons locked behind a payment • The free version shows ads: a banner on the Learn and Review screens, and now and then a full-screen ad after you finish a lesson, review, quiz, drill, story, conversation, dialogue or game. Never during one. LEARN THROUGH YOUR OWN LANGUAGE Explanations, hints and translations are in the language you choose: 33 languages, including English, Chinese, Hindi, Arabic, Portuguese, Russian, Japanese, Korean, French and German. The Spanish you learn is the same in every language. REAL GRAMMAR, EXPLAINED • A plain-language explanation opens every lesson: why the words behave that way, not just what to tap • Ser vs estar, the subjunctive, por vs para: the hard things get the space they need • A searchable grammar library you can come back to any time • Read aloud: hear an explanation in your language, on phones that have a voice for it SPEAK IT, TYPE IT, HEAR IT • Speaking exercises use your phone's speech recognition and show you what they heard. They are always optional. • Typed answers, not only multiple choice, with a keyboard bar for accents • Every Spanish word and sentence is spoken by your phone's built-in voice PRACTICE THAT STICKS • Smart Review brings each word back just before you would forget it (spaced repetition based on SM-2) • Fix Your Misses turns the exercises you got wrong into a short session • Daily Workout: up to twelve items, once a day, from your due words and recent mistakes • 12 dialogues: two people talk, each in their own voice; tap any word for its meaning, then answer questions • Three games: Pares, Palabras and A Day in Mexico City, a 3D story where you reply in Spanish • 24 graded stories: tap any word for its meaning and audio • 18 conversations that correct you and explain why • Conjugation Gym: 64 verbs, seven tenses, drills and Fill the chart • Over 1,200 words and phrases • Flashcards for every unit, plus cards and quizzes you build yourself • A 164-phrase phrasebook for travel, food, work and small talk WORKS OFFLINE The whole course ships inside the app. No account, no sign-up. Lessons, stories and review work without a connection. Audio needs a Spanish voice on your phone, and speaking practice works offline only where your phone can recognize Spanish on the device. YOUR PROGRESS STAYS ON YOUR PHONE Streaks, XP, a 14-day chart and an achievement wall. There is no account and no server of ours: your progress is stored on your phone, and we never receive it. Export a backup file and import it on another phone or tablet; importing merges and never deletes. PRIVACY The app goes online only for ads in the free version (Google AdMob), for purchases through Apple and, on some phones, for speech recognition. The app never records or keeps your voice; depending on your phone, Apple may process the audio to recognize it. HOW THE COURSE IS MADE The course was written by AI and checked with automated tests and AI review, not by a human linguist. Translations other than English are machine-generated. PRO (OPTIONAL SUBSCRIPTION) Pro removes the ads. Nothing else is locked behind it: every lesson is free for everyone. • Pro Monthly: $0.99 a month • Pro Yearly: $5.99 a year Payment is charged to your Apple Account at confirmation of purchase. The subscription renews automatically at the same price unless you cancel at least 24 hours before the end of the current period. Manage or cancel anytime in Settings › your name › Subscriptions. Prices shown are US pricing; your local price appears in the app. Terms of Use: https://www.apple.com/legal/internet-services/itunes/dev/stdeula/