How often and when has a term been used ?

On a mailing list I am a member of, I just found mentioned this tool:

It is available for a couple of languages and shows at which time the term searched for has been used how often.

It seems to have gone through the blogging world a few years before, but I had never heard about it, and found it quite interesting. Good for linguists as well as sociocultural research indeed. I tried (having written my thesis about human dignity and international law) “dignity”, and found the result rather unexpected at first.