 <p>There's an old joke about two people at a natural history museum wondering how old a dinosaur fossil is. A guard overhears them and says, "Oh, it's five-hundred million and seven years old". One of the people says, "that's an astonshing number, how was it determined?" The guard says, "Well, I was told it was five-hundred million years old during my orientation, and that was seven years ago."</p> <p>This is the result of adding together two times with differing levels of precision. Say I start a clock at 12:03:06 and that clock only has minute resolution. If I add the time on my clock to the start time, I'll get a series of times like 12:03:06, 12:04:06, 12:05:06, and so on.</p> <p>Windows is adding the time from a monotonic clock with millisecond resolution and an arbitrary start time to the time at which that clock read zero with microsecond resolution.</p> <p>A common technique is simply to round the time to the resolution you are relying on, which of course must not be higher than the clock's guaranteed resolution. I believe the guaranteed resolution for this clock is 10 milliseconds.</p>