Q: NSTimer and Animation synced I'm doing a countdown timer using NSTimer and a circle Animation like this one: GitHub.
My first question is: What CAMediaTimingFunction is for?
My second and most important question is: I'm getting NSTimer and my animation out of sync. Typically the timer reaches 0 before the animation. What is the best approach on this situation? 

A: One way to be sure you are in sync is not using core animation, but setting the strokeEnd manually in the timer callbacks. I would suggest using a CADisplayLink instead of the NSTimer since it is bound to the refresh rate of the display.
Use its timestamp to calculate how much time passed and set the label text and the circle's strokeEnd appropiately.
