title: iPhone timer with minimal error/drift
body: <p>I'm looking to create functionality that gets repeated very quickly - around 50ms. I need, however, as much consistency as possible in the call and I have found NSTimer to be a bit erratic. It seems I might find some help with keeping time from <a href="https://stackoverflow.com/questions/1450737/what-is-mach-absolute-time-based-on-on-iphone">mach_absolute_time</a>. Any tips on using this to create an extremely accurate timer?</p>