How accurate of DateTime.Now

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DateTime.Now is not intended to be a high-precision timer. For Windows NT 3.5, Windows 2000 and later, it has a resolution of approximately 10–15 milliseconds. Resolution may be lower on other platforms. For more accurate timing, the System.Diagnostics.StopWatch class is available. Other high-precision timers include the kernel32.dll QueryPerformanceTimer and QueryPerformanceFrequency native calls. If you are trying to time the execution speed of code, an even better solution is just to use ANTS Performance Profiler.