Here are 3 references CW students may find interesting:
http://www.fists.org The International Morse Preservation Society. A large website of a club dedicated to cw around the world. Check out Newsletters of “Americas” site for articles on keys (2015, Issue 2: 2013, Issue 1).
Article by N2DE, “The Anatomy of a Paddle”. Great intro explaining mechanical features of a good paddle. CAUTION; Focuses on high-end paddles…can be addictive!! ALSO, Goggle other articles by N2DE.