Cookie Policy

Cookies are small text files a website stores on your device. They let a site remember things between visits — that you are signed in, that you prefer dark mode — and they let analytics and advertising services recognise a returning browser.

• Essential — sign-in sessions and security. The site cannot work without these.
• Preference — your theme choice and recently viewed subjects, so the site looks the same when you come back.
• Analytics — Google Analytics, which tells us in aggregate which pages are used and which are ignored.

Your theme choice and recently viewed subjects are kept in your browser's own storage and are never sent to us.

This site shows ads through Google AdSense, and those ads rely on cookies set by Google and other advertising vendors rather than by us.

• 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 visit to this site and/or other sites on the internet.
• These cookies are set under the advertiser's own domain. We cannot read them and we cannot delete them for you.

You can opt out directly with Google or across the wider advertising industry:

• Google Ads Settings — opt out of personalised ads
• How Google uses cookies in advertising
• aboutads.info — opt out of third-party vendor cookies

• Firebase (Google) — keeps you signed in
• YouTube (Google) — remembers player preferences on embedded videos
• Google Drive (Google) — opening a study file is a request to Google, under Google's own cookie policy

• Session cookies are deleted when you close your browser
• Persistent cookies remain for a set period, up to one year
• Authentication cookies last as long as your sign-in session

Every major browser lets you block or delete cookies. You can usually:

• Block all cookies, which will stop sign-in from working
• Delete cookies already stored
• Allow cookies only from sites you choose
• Block third-party cookies while keeping first-party ones

Blocking advertising and analytics cookies does not stop you reading anything on this site. All the study material is open without an account.

We may update this policy as the services we use change. The revision date at the top of this page reflects the most recent change.