Sin of PI is not even close to 0 on iphone

Did you make sure you were using radians and not degrees? Seems fine for me.

Sin PI = 0.05480366514879

If I use Calculator (or indeed PCalc) in radians mode, sin(PI) = 0. In degrees mode, sin(PI) = 0.0548[etc].

Check your units. Many calculators default to degrees for angle entries.