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When you browse or use this website in any other way, you are agreeing to these terms. If you do not accept these terms, please click here to leave this website immediately.


The information on this website is prepared with care and provided in good faith, for general educational purposes, for free. However, I, Chris Woodford, do not warrant that any of the information published on is accurate, correct, up-to-date, or complete. I make no representations or warranties of any kind, express or implied, about the text or other content on this site and (to the extent permitted by applicable law) I accept no responsibility for any loss, damage, or injury that may arise if you use any text or any other content that may be published here. Please be aware that you use the information from this website at your own risk.

This website contains photographs of real-world products purely for illustrative purposes and occasionally mentions products and brands in the text by way of example. The inclusion of a photograph, or textual reference to a product or brand, does not represent any endorsement of that product or brand or any endorsement by the product manufacturer or brand owner of this website or anything I may say in the text. Similarly, on pages where photos sourced from third parties (such as US Federal government agencies) are used, that does not imply or constitute endorsement by those parties. On all pages where US military photos ("US Department of Defense (DoD) visual information") are used on this website, the following disclaimer also applies: "The appearance of US Department of Defense (DoD) visual information does not imply or constitute DoD endorsement." In line with the US FTC Guidelines on Endorsements, I am very happy to clarify that I have never accepted (and will never accept in the future) any money, gifts, or anything else of any kind from any companies or individuals in return for writing about or otherwise featuring products on this website.

Privacy and cookies

Our website does not collect or store any personal information about you. It does not use persistent "cookies" (small files stored on your computer that last beyond your current session) or any other tracking mechanisms (transparent GIFs, web beacons, and so on). However, most of our pages display advertisements and the advertising companies we work with try to serve relevant and useful advertisements to our readers by storing what are known as third-party cookies on your computer. Most of our pages also contain the Facebook "Like", which may set third-party cookies on your computer.

For more, please see our detailed privacy policy page.

© Copyright

This is our formal copyright and legal notice covering all the material we publish on You might also like to read our general guide to using material from this website. The simplest way to avoid any kind of legal problem for yourself or your organization is to ask for permission before you use something. Please do feel entirely free to contact us if you have any queries, you'd like to discuss reprinting or reusing our articles, or you'd like us to confirm whether some use you have in mind is "fair use" or otherwise okay. We are always happy to help—and generally we'll reply within a day or so.


All the text on Explain that Stuff is copyright © Chris Woodford (with copyright dates as indicated on each page) and all rights are reserved. Unauthorized use of text from this website on other websites (and elsewhere) is an infringement of copyright under international laws that apply in most countries, including (but not limited to) Title 17 of the United States Code USC section 501, et seq. (including the Digital Millennium Copyright Act), the Copyright Designs and Patents Act (1988) in the UK, the Copyright & Related Rights Act 2000 (Ireland), and copyright laws that apply in most other countries through the Berne Convention and other international treaties. Text from this website is registered (or deposited pending registration) at the US Copyright Office, so under section 504(c)(2), willful copyright infringement could make you liable to statutory damages of up to $150,000 per work infringed. You may browse and download information from this website for your own personal use. You are not permitted to copy, broadcast, download, upload, store (in any medium), transmit, translate, distribute, show or play in public, adapt or change in any way the text of web pages for any other purpose whatsoever without the prior written permission of the copyright owner (Chris Woodford).

Fair use (also known as "fair dealing"), such as briefly quoting from articles on this website for purposes of commentary or discussion, is fine, but you must attribute this website as the source (in some legal jurisdictions, this is referred to as giving "sufficient acknowledgement") and not pass off our work as your own.

If you are teacher or professional educator, you are most welcome to print and circulate copies of our articles as handouts or other teaching materials for your own classes, within your own school. You do not need to ask permission, but please kindly credit this website as your source. We consider this a fair use—and something we would warmly endorse and encourage. However, please kindly do not copy articles verbatim onto publicly accessible school or educational websites. These create inferior substitutes for the original articles (copies are not regularly checked, improved, and updated) and we will consider them copyright infringement.

Under Title 17 of the United States Code USC section 506 and section 1202, it can be a criminal offence to intentionally remove copyright management information (CMI), including copyright notices and copyright ownership information, from copyright works. If you copy articles from this website and remove the copyright notice, or paste a copyright notice of your own onto something you have copied from this website, you could be committing a criminal offence. The penalty for doing this for commercial advantage or private financial gain can be a fine of up to $500,000 or imprisonment for up to five years. So don't do it!

For the purposes of section 78 of the Copyright Designs and Patents Act (1988) in the UK, and other international copyright laws, Chris Woodford has asserted all his moral rights as the author of the text published on this website, including (but not limited to) his right to be identified as the author, his right to object to derogatory treatment of his work, and his right to object to false attribution.

You may not use any material from this website to suggest or imply that I endorse or approve of you, your organization or company, your website, or any product or service you might be producing or selling. (Relevant United States code here includes 15 U.S. Code §1125—False designations of origin, false descriptions, and dilution forbidden.)


Images created by are copyright © Chris Woodford (Explain that, but published under this Creative Commons License (briefly: you are very welcome to reuse them online or offline, for noncommercial purposes only, under the terms of this licence providing you attribute the images to "Explain that Stuff".

Images used on this website that are credited to US Federal Government agencies are believed, in good faith, to have been "prepared by an officer or employee of the United States Government as part of that person's official duties" and therefore (under section 105) considered to be in the public domain.

All drawings of original patents have been reproduced from the US Patent and Trademark Office database (and generally downloaded via Google Patents). Unless otherwise noted, patent drawings are believed to be in the public domain per the USPTO's Editorial Standards guidelines, which state that (subject to limited exceptions) "the text and drawings of a patent are typically not subject to copyright restrictions."

Other images are copyright their creators and are always used by permission or under a particular Creative Commons licence, as noted in the image caption.

If you are the manufacturer of a product and you'd prefer it not to be featured in one of our photos, please contact me.

It is our policy always to respect the right to privacy of people shown in photographs, so faces and heads are either cropped out of pictures, pixelated, blurred, or otherwise disguised.

Artificial intelligence

You may not use data mining, machine-learning, artificial intelligence, or similar data processing tools to process text, images, or other data from this website without the express written consent of the copyright holder (Chris Woodford).


It is our policy to credit inventors for their creative work by acknowledging trademarks and registered trademarks wherever possible. Where a trademark is used in an article, we have tried to indicate this with a ® or ™ symbol (on first occurrence) and note the ownership of the trademark just below the copyright notice at the bottom of the page. If we have used a trademark incorrectly, please let us know and we will be delighted to make corrections at the earliest opportunity (generally the same day).

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