Ben Pridmore on Daniel Tammet

"It's well known that he uses memory techniques like a 'regular person' - he was a regular at the world championships for years, slightly before my time (though we did meet in 2000), and always talking about the specific techniques he used. It's not really that much of a secret..."

Ask a memory champion.

Mnemotechnics.org
http://mnemotechnics.org/forums/ask-a-memory-champion-3839.html?page=1

By the way, did I mention that I wrote a book about Daniel Tammet?

Daniel Tammet: the Boy with the Incredible Story.
by Lili Marlene
published by Smashwords in 2013
https://www.smashwords.com/books/view/288635