private static TimeUnit chooseUnit(long nanos) {
		if (DAYS.convert(nanos, NANOSECONDS) > 0) {
			return DAYS;
		}
		if (HOURS.convert(nanos, NANOSECONDS) > 0) {
			return HOURS;
		}
		if (MINUTES.convert(nanos, NANOSECONDS) > 0) {
			return MINUTES;
		}
		if (SECONDS.convert(nanos, NANOSECONDS) > 0) {
			return SECONDS;
		}
		if (MILLISECONDS.convert(nanos, NANOSECONDS) > 0) {
			return MILLISECONDS;
		}
		if (MICROSECONDS.convert(nanos, NANOSECONDS) > 0) {
			return MICROSECONDS;
		}
		return NANOSECONDS;
	}
Returns a string representation of the current elapsed time.
shared/src/main/java/com/oasisfeng/perf/Stopwatch.java