There are two print books available - one printed in the UK and the other in the US. The UK is a traditional book in the sense there are a batch printed in advance. The US book is a print on demand book and so in theory would never be out of stock.
UK: Best place to purchase is from the Matador web shop as they are the publishers and so will always be in stock as long as in print.
http://www.troubador.co.uk/book_info.asp?bookid=1353
Amazon.co.uk
http://www.amazon.co.uk/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=Diagonal+lengths
US: Best place to purchase it is from the CreateSpace web shop.
https://www.createspace.com/3502061
Amazon.com
http://www.amazon.com/Diagonal-Lengths-Rethinking-Our-World/dp/1456368699/ref=sr_1_1?ie=UTF8&qid=1293494658&sr=8-1
International: Please purchase it from Create Space.
https://www.createspace.com/3502061
I also have an eBook available on the Kindle format available form Amazon.com and Amazon.co.uk
(Note: the pdf for the eBook was uploaded and converted automatically to Kindle e-Book format. It should be ok as the conversion was successful, however I've learnt the automatic conversion can get mixed up converting tables of data and as a precaution am getting a team at Amazon to do a manual conversion. Once it's done and uploaded, I'll remove this note)
