A record kept in identical copies by many computers, so old entries cannot be quietly changed. Useful when nobody trusts a single keeper; slower than a database otherwise.
The drawing that proves the sentence above. It is the same card that is in the book.
Think of it as
a ledger written in ink, copied to a thousand desks.
For example
The same list is kept on thousands of computers at once. To change yesterday's entry you would have to change it on all of them.
This is one card out of 275.
The hundred words you meet most are free — the whole set, animated, in one file that works with no internet.
Volume 1 has all 275 in fifteen chapters, with Staying Safe the largest chapter on purpose.