Transparency
Sources and methodology
How we research, write, check and score, and where every claim comes from.
How we choose sources
Each article is built from sources we can open, read and cite. We give priority to primary and institutional material: standards bodies, government agencies, national laboratories, universities, museums and libraries. Reference works and specialist publications are used to fill gaps, never as the only support for an important claim.
Every article ends with the list of sources behind it. Every quiz question is tied to one of those sources, and the link appears on the answer screen.
How articles are written
- Research. We read the sources and identify the underlying principle, the history and the limits of each technology.
- Drafting. We explain how it works step by step, add everyday examples and address common misconceptions.
- Fact check. Numbers, dates, names and technical claims are checked against the cited sources before publication.
- Review dates. Each article shows when it was published and when it was last reviewed.
How quiz questions are built
- Each question tests one clear, verifiable fact or idea. We do not use trick questions, opinions or unsourced claims.
- We avoid facts that age quickly, such as records, prices, new product releases and market statistics.
- Each question has four plausible options, one indisputably correct answer, and an explanation of two to four sentences.
- Each question links to the article it comes from and to the source that supports the answer.
- Questions are unique. We do not repeat or rephrase a question within the bank.
Difficulty levels and scoring
- Easy (10 points): widely known concepts and basic ideas.
- Medium (15 points): understanding how a mechanism works.
- Hard (20 points): details, history, limits and less obvious consequences.
Your percentage is the share of correct answers. Points reward harder questions. Records are stored only on your device, and there are no public rankings. In games with a single category and a single difficulty level, a small number of questions may come from the nearest difficulty level to complete a 20- or 30-question game; the quiz tells you when this happens.
The daily challenge
The daily challenge selects ten questions from the full bank using the calendar date as the only input, so everyone sees the same set on the same date. It needs no server and no account.
Sources by article
This is the complete list of sources used in the articles, grouped by category. Links open the original pages in a new tab.
Computers and Devices
Why Keyboards Use the QWERTY Layout · 6 quiz questions · 3 sources
- The Origins of the QWERTY Keyboard — Smithsonian Magazine
- Christopher Sholes — Lemelson-MIT Program
- Typewriter — Encyclopaedia Britannica
Why the Save Icon Is a Floppy Disk · 6 quiz questions · 3 sources
- 1976: Minicomputers stimulate floppy disk sales — Computer History Museum
- Floppy disk (Input and Output, Revolution) — Computer History Museum
- Alan F. Shugart — Computer History Museum
How a Touchscreen Detects Your Fingers · 6 quiz questions · 4 sources
- The first capacitative touch screens at CERN — CERN Courier
- CERN touch screen — Symmetry Magazine (Fermilab and SLAC)
- How do touch-sensitive screens work? — MIT School of Engineering
- Touch Screens: How our devices moved beyond buttons — Illumin Magazine, USC Viterbi School of Engineering
How Biometric Scanners Work · 6 quiz questions · 6 sources
- Biometrics — National Institute of Standards and Technology (NIST)
- Fingerprint Recognition — National Institute of Standards and Technology (NIST)
- Iris Exchange (IREX) Overview — National Institute of Standards and Technology (NIST)
- Face Technology Evaluations (FRTE/FATE) — National Institute of Standards and Technology (NIST)
- Using 'Minutiae' to Match Fingerprints Can Be Accurate — National Institute of Standards and Technology (NIST)
- How Iris Recognition Works — John Daugman, University of Cambridge (IEEE Transactions on Circuits and Systems for Video Technology, 2004)
Common Tech Myths Explained with Evidence · 6 quiz questions · 6 sources
- What Private Browsing Does and Doesn't Do — Mozilla Firefox
- Maximizing Battery Lifespan and Performance — Apple
- Cell Phones and Cancer Risk — National Cancer Institute, National Institutes of Health
- Concepts overview (page cache and reclaimable memory) — The Linux Kernel documentation
- Resolution and Light Sensitivity Tradeoff with Pixel Size — Stanford University (SPIE Proceedings, 2006)
- Away From Prying Eyes: Analyzing Usage and Understanding of Private Browsing — Carnegie Mellon University (SOUPS 2018, USENIX)
Internet and Connectivity
What Airplane Mode Really Does · 8 quiz questions · 6 sources
- 47 CFR 22.925 - Prohibition on airborne operation of cellular telephones — Electronic Code of Federal Regulations (U.S. Government Publishing Office / National Archives)
- Expanding Access to Mobile Wireless Services Onboard Aircraft (Notice of Proposed Rulemaking) — Federal Communications Commission, via the Federal Register
- 14 CFR 91.21 - Portable electronic devices — Electronic Code of Federal Regulations (U.S. Government Publishing Office / National Archives)
- GPS — National Aeronautics and Space Administration
- Cell Phone Interference — Physics Van, University of Illinois Urbana-Champaign
- Bluetooth Technology Overview — Bluetooth Special Interest Group
How Bluetooth Connects Nearby Devices · 8 quiz questions · 4 sources
- Bluetooth Technology Overview — Bluetooth Special Interest Group
- Origin of the Bluetooth Name — Bluetooth Special Interest Group
- Bluetooth Security — Bluetooth Special Interest Group
- Bluetooth — Encyclopaedia Britannica
What Storing Files in the Cloud Really Means · 7 quiz questions · 3 sources
- The NIST Definition of Cloud Computing (SP 800-145) — National Institute of Standards and Technology
- Security Guidelines for Storage Infrastructure (SP 800-209) — National Institute of Standards and Technology
- Cloud Computing Synopsis and Recommendations (SP 800-146) — National Institute of Standards and Technology
How Encryption Protects Information · 7 quiz questions · 4 sources
- Advanced Encryption Standard (AES), FIPS 197 — National Institute of Standards and Technology
- RFC 8446: The Transport Layer Security (TLS) Protocol Version 1.3 — Internet Engineering Task Force
- Public Key Cryptography (glossary) — NIST Computer Security Resource Center
- Encryption — Encyclopaedia Britannica
Everyday Inventions
How Rechargeable Batteries Store Energy · 5 quiz questions · 3 sources
- Lithium-ion battery — Wikipedia
- Rechargeable battery — Wikipedia
- The Nobel Prize in Chemistry 2019 — Royal Swedish Academy of Sciences
What Happens During Fast Charging · 5 quiz questions · 3 sources
- Fast charging (battery charging principles) — Wikipedia
- Lithium-ion battery — Wikipedia
- Charging Electric Vehicles at Home — U.S. Department of Energy, Alternative Fuels Data Center
How Solar Panels Turn Light into Electricity · 5 quiz questions · 4 sources
- Photovoltaics and Electricity — U.S. Energy Information Administration
- April 25, 1954: Bell Labs Demonstrates the First Practical Silicon Solar Cell — American Physical Society
- Milestones: First Practical Photovoltaic Solar Cell — Engineering and Technology History Wiki (IEEE)
- Solar cell — Wikipedia
How LED Bulbs Produce Light · 5 quiz questions · 5 sources
- LED Lighting — ENERGY STAR (U.S. EPA and U.S. DOE)
- The Nobel Prize in Physics 2014 — Royal Swedish Academy of Sciences
- The Birth of the Visible LED: Nick Holonyak Jr. and a Turning Point in Photonics — IEEE Photonics Society
- LED Basics — U.S. Department of Energy
- Light-emitting diode — Wikipedia
How a Microwave Oven Heats Food · 5 quiz questions · 4 sources
- Microwave Oven Radiation — U.S. Food and Drug Administration
- Percy Spencer — MIT Lemelson-MIT Program
- Microwave oven — Wikipedia
- Cavity magnetron — Wikipedia
How an Induction Cooktop Works · 5 quiz questions · 3 sources
- Induction cooking — Wikipedia
- Electromagnetic induction — Wikipedia
- Eddy current — Wikipedia
Image, Sound and Media
How a QR Code Stores Information · 6 quiz questions · 4 sources
- The history of QR Code — DENSO WAVE
- Standardization of QR Code — DENSO WAVE
- Tutorial on Reed-Solomon error correction coding (NASA TM-102162) — NASA Technical Reports Server
- Empowering Digital Communications — MIT Lincoln Laboratory
How Barcodes Are Scanned · 6 quiz questions · 3 sources
- The History of the Bar Code — Smithsonian Magazine
- Number Theory and Cryptography II. Check Digits — Cornell University Department of Mathematics
- Supermarket Scanner — Smithsonian Institution, National Museum of American History
How Compression Shrinks Files · 6 quiz questions · 3 sources
- RFC 1951: DEFLATE Compressed Data Format Specification version 1.3 — IETF / RFC Editor
- Portable Network Graphics (PNG) Specification (Third Edition) — W3C
- JPEG (ISO/IEC 10918) overview — Joint Photographic Experts Group
How Noise-Cancelling Headphones Reduce Sound · 6 quiz questions · 3 sources
- How Do Active Noise Canceling Headphones Work? — Scientific American
- US Patent 2,043,416: Process of Silencing Sound Oscillations — Google Patents (USPTO record)
- How Do Noise-Canceling Headphones Block Sound? — How Everything Works
How Digital Camera Sensors Capture Images · 6 quiz questions · 3 sources
- CMOS Image Sensors — Evident Scientific (Olympus)
- The Invention and Early History of the CCD (Nobel Lecture) — Nobel Prize Outreach
- The Charge-Coupled Device: Revolutionizing How Astronomers See the Universe — NOIRLab
Space and Communication
How Wi-Fi Transmits Data · 6 quiz questions · 4 sources
- IEEE 802.11 Wireless Local Area Networks — IEEE 802 LAN/MAN Standards Committee
- Discover Wi-Fi — Wi-Fi Alliance
- Milestone-Proposal: Orthogonal Frequency-Division Multiplexing (OFDM) with error correction for wireless networks, 1992 — Engineering and Technology History Wiki (IEEE)
- Wireless LANs, in An Introduction to Computer Networks — Loyola University Chicago
Why GPS Depends on Extremely Precise Clocks · 6 quiz questions · 5 sources
- Global Positioning System (GPS) — NASA Space Communications and Navigation
- Space Segment — GPS.gov
- The Second — National Institute of Standards and Technology
- Real-World Relativity: The GPS Navigation System — Ohio State University Department of Astronomy
- Putting Einstein to the Test With the World's Most Accurate Clocks — National Institute of Standards and Technology
How Fiber Optics Carry Information as Light · 6 quiz questions · 3 sources
- Total Internal Reflection — The Fiber Optic Association
- Milestones: Trans-Atlantic Telephone Fiber-Optic Submarine Cable (TAT-8), 1988 — Engineering and Technology History Wiki (IEEE)
- Transatlantic Optical Cable — Engineering and Technology History Wiki (IEEE)
How Undersea Cables Keep the Internet Connected · 6 quiz questions · 3 sources
- Submarine Cables — National Oceanic and Atmospheric Administration
- Milestones: Trans-Atlantic Telephone Fiber-Optic Submarine Cable (TAT-8), 1988 — Engineering and Technology History Wiki (IEEE)
- Transatlantic Optical Cable — Engineering and Technology History Wiki (IEEE)
How Satellites Enable Long-Distance Communication · 6 quiz questions · 5 sources
- What Is a Satellite? — NASA
- Catalog of Earth Satellite Orbits — NASA Earth Observatory
- NASA Launches Telstar — Engineering and Technology History Wiki (IEEE)
- Commercial Communications Satellites — U.S. Centennial of Flight Commission
- Tracking and Data Relay Satellite (TDRS) — NASA NSSDCA
Robotics and Machine Intelligence
How a 3D Printer Builds Objects · 6 quiz questions · 4 sources
- Additive Manufacturing — National Institute of Standards and Technology (NIST)
- Measurement Science for Additive Manufacturing Program — National Institute of Standards and Technology (NIST)
- Stereolithography — Wikipedia
- Fused filament fabrication — Wikipedia
How Drones Stay Stable in Flight · 6 quiz questions · 4 sources
- Aircraft Rotations — NASA Glenn Research Center
- Quadcopter — Wikipedia
- PID controller — Wikipedia
- Inertial measurement unit — Wikipedia
How Robots Perceive Their Surroundings · 6 quiz questions · 5 sources
- Lidar — Wikipedia
- Simultaneous localization and mapping — Wikipedia
- Sensor fusion — Wikipedia
- Rover Components: Perseverance — NASA Science
- Intelligent Systems Division — National Institute of Standards and Technology (NIST)
How Voice Assistants Recognize Commands · 6 quiz questions · 3 sources
- Speech recognition — Wikipedia
- Mel-frequency cepstrum — Wikipedia
- Speech and Language Processing (3rd edition draft) — Stanford University
How Recommendation Systems Learn Preferences · 6 quiz questions · 3 sources
- Recommender system — Wikipedia
- Netflix Prize — Wikipedia
- Collaborative Filtering (Recommendation Systems course) — Google for Developers
Found a problem?
If a source is unavailable, a fact looks wrong or a question is unclear, please tell us through the contact page. Our process is described in the Corrections policy.