Privacy policy

What is collected when you visit

No account is needed to read anything here, and the site does not set cookies of its own for visitors. The server records each page view so the owner can see which pages are read and where readers come from. For each view it stores:

• the page address, the time, and the address of the page that linked to it (the referrer);
• your IP address and your browser's user-agent string;
• an approximate location (country, region, city) worked out from the IP address using a lookup table held on the server, so your address is not sent to any location service;
• a pseudonymous visitor id, which is a one-way hash of the IP address and user-agent, used to count unique visitors.

These records are visible only to the site owner, are not sold or shared, and are deleted automatically after 60 days.

The contact form

If you send a message through the contact form, the name, email address, subject and message you enter are stored so the owner can read and reply to them. They are not used for anything else, not added to any mailing list, and not shared. Ask through the same form to have a message deleted.

The SIGMA assistant

The chat assistant on the portfolio page answers questions about the owner's professional background. The text you type is sent to Groq, which runs the language model that writes the answer. This site does not store the conversation. Do not type personal or confidential information into it.

Storage in your browser

Flashcard progress, study streaks and similar preferences are kept in your browser's local storage so they survive a reload. They stay on your device, are never sent to the server, and are removed when you clear your browser's site data.

Advertising and cookies from Google

This site shows advertisements served by Google AdSense, which helps pay for keeping the library free. Google and its partners use cookies and similar technologies to serve and measure those ads:

• Third-party vendors, including Google, use cookies to serve ads based on your prior visits to this website or other websites.
• Google's use of advertising cookies enables it and its partners to serve ads to you based on your visits to this site and/or other sites on the Internet.
• You can opt out of personalised advertising in Google Ads Settings, and out of some third-party vendors' use of cookies for personalised advertising at aboutads.info or, in Europe, youronlinechoices.eu.

Google explains how it uses information from sites that show its ads in How Google uses information from sites or apps that use our services, and describes its advertising cookies in Advertising. Where the law requires it (for example in the European Economic Area, the United Kingdom and Switzerland), you are asked for consent before personalised ads are shown, and you can change that choice at any time from the privacy link the consent message leaves on the page.

Other services pages load from

Pages load fonts from Google Fonts, and some load diagram and maths rendering scripts from the jsDelivr content network. Like any web server, those services receive your IP address when your browser fetches a file from them. Links to other sites, including the headlines in the news feeds, lead to pages this site does not control; their own privacy policies apply.

Children

The site is written for working engineers and students and is not directed at children under 13. It does not knowingly collect information from them.

Your choices

You can read everything here with cookies and scripts blocked. To ask what is held about you, or to have it corrected or deleted, use the contact form or write to sigmoidptn@gmail.com.

Changes to this policy

If what the site collects changes, this page changes with it and the date at the top is updated. See also the terms of use.