This http://www.amazon.com/Mel-Guitar-Technic...uitar+technic#_
is an excellent book that includes that exercise plus a lot of other guitar technique exercises.

I have had a copy since about 1963 and in fact just had to order a new one as the old one was worn out.

This is one book that should be in every guitarist’s collection.

Whenever I get something stuck in the back of my throat, I dislodge it by drinking a beer.
It's called the Heineken Maneuver.

64 bit Win 10 Pro, the latest BiaB/RB, Roland Octa-Capture audio interface, a ton of software/hardware