About The Ads
This website pays its bills with money from advertising.
The site is otherwise free to use. No subscriptions or charges.
We don't collect user data, but the ad publishers may do so, for ad personalization and measurement. Read more about this, including how to turn it off.
Ads can sometimes be distracting, so you can hide them for 36 hours (yes they come back, but you can hide them again).
Handy for classroom demonstrations!
Click on the "Hide Ads" near the top right, and a small "cookie" gets automatically set so other pages on this site will know your choice.
Seen An Ad You Don't Like?
Our ads come from Google, and there are filters in place, but sometimes a bad ad slips through.
So please let us know of any ad you don't think should be there. Give as many details as possible (name and web address of advertiser etc) so it can be identified and blocked.