Amazon UK is selling the paper version of my book, Arduino Interrupts, at a 42% discount for some reason. The paper book is currently £11 cheaper than the Kindle version. A good cure for insomnia!
It's nicer to support your local bookshop of course, but sadly these days, almost none (in the UK at least) carry Computer books now. I used to buy them whenever I was in Borders, Waterstones, and a couple of Aberdeen independent bookshops, but all gone now.
https://www.amazon.co.uk/Arduino-Interr ... mp_s_a_1_3