the value returned by ofGetFrameRate() is very filtered so you shouldn't rely on that to animate. the best value in order to integrate the animation is ofGetLastFrameTime() which returns the time for the last frame in seconds. so you can do:
x+=ofGetLastFrameTime() * speed;where speed is usually expressed in pixels/s
can you point where in the book it says that? it's really not correct and we should fix it