Measuring Time Accurately in Swift for Comparison Across Devices

Question

I need to be able to record reaction time, from when the screen loads or the question label refreshes until the user taps a number button. I\'m not finding documentation fro

Answer 1

As already said, the precision of NSDate() is probably good enough for your purpose. Just for the sake of completeness, mach_absolute_time() from the referenced Technical Q&A QA1398 works in Swift as well:

let t1 = mach_absolute_time()
// do something
let t2 = mach_absolute_time()

let elapsed = t2 - t1
var timeBaseInfo = mach_timebase_info_data_t()
mach_timebase_info(&timeBaseInfo)
let elapsedNano = elapsed * UInt64(timeBaseInfo.numer) / UInt64(timeBaseInfo.denom);
print(elapsedNano)

Possible advantages of this method:

• Calling mach_absolute_time() seems to be much faster than calling NSDate().timeIntervalSinceReferenceDate, so this method might be better suited to measure extremely short intervals.
• The value of NSDate() changes if the clock is adjusted, mach_absolute_time() does not have this problem.