Cocoa Design Patterns
Learning OpenGL ES for iOS
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    Cocoa Design Patterns
    by Erik M. Buck, Donald A. Yacktman
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    Learning OpenGL ES for iOS: A Hands-on Guide to Modern 3D Graphics Programming
    by Erik M. Buck

Errata > (Kindle) The statement "Normal vectors are also unit vectors" is incorrect

There can be a normal vector that is not normalized in which case it is not a unit vector (http://mathworld.wolfram.com/NormalVector.html).
The sentence is in Chapter 4. "Shedding Some Light"
August 11, 2012 | Unregistered CommenterRobert
Thank you for your post. You are correct that any vector perpendicular to a plane is a normal vector for that plane. However, in the context of OpenGL lighting equations, normal vectors must also be unit vectors.
August 13, 2012 | Registered CommenterErik Buck