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Both System.Timers.Timer and System.Threading.Timer fire at intervals that are considerable different from the requested ones. For example: new System.Timers.Timer(1000d / 20); yields a timer that fires 16 times per second, not 20. To be sure that there are no side-effects from too long event handlers, I wrote this little test program: int[] frequencies = { 5, 10, 15, 20, 30, 50, 75, 100, 200, 500 }; // Test System.Timers.Timer foreach (int frequency in frequencies) { int count = 0; // Initialize timer System.Timers.Timer timer = new System.Timers.Timer(1000d / frequency); timer.Elapsed += delegate { Interlocked.Increment(ref count); }; // Count for 10 seconds DateTime start = DateTime.Now; timer.Enabled = true; while (DateTime.Now < start + TimeSpan.FromSeconds(10)) Thread.Sleep(10); timer.Enabled = false; // Calculate actual frequency Console.WriteLine( "Requested frequency: {0}\nActual frequency: {1}\n", frequency, count / 10d); } The output looks like this: Requested: 5 Hz; actual: 4,8 Hz Requested: 10 Hz; actual: 9,1 Hz Requested: 15 Hz; actual: 12,7 Hz Requested: 20 Hz; actual: 16 Hz Requested: 30 Hz; actual: 21,3 Hz Requested: 50 Hz; actual: 31,8 Hz Requested: 75 Hz; actual: 63,9 Hz Requested: 100 Hz; actual: 63,8 Hz Requested: 200 Hz; actual: 63,9 Hz Requested: 500 Hz; actual: 63,9 Hz The actual frequency deviates by up to 36% from the requested one. (And evidently cannot exceed 64 Hz.) Given that Microsoft recommends this timer for its "greater accuracy" over System.Windows.Forms.Timer , this puzzles me. Btw, these are not random deviations. They are the same values every time. And a similar test program for the other timer class, System.Threading.Timer , shows the exact same results. In my

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