在单步调试的时候TimeSpan和StopWatch的值会有很大差别，可是如果断点设置在方法末尾直接运行到断点地方，这时再看TimeSpan和StopWatch的值相等，即使不等差距也很小？求解释，万分感激！

        Stopwatch stopWatch = new Stopwatch();
        stopWatch.Start();

        DateTime startTime = DateTime.Now;

        Thread.Sleep(1000);
        stopWatch.Stop();

        DateTime endTime = DateTime.Now;
        TimeSpan timeSpan = startTime.Subtract(endTime).Duration();
        int timeSpanDValue = (int)timeSpan.TotalMilliseconds;

        int stopWatchTimeDValue = (int)stopWatch.ElapsedMilliseconds;