[hannes69]

OMG! Thank you! One frame drop every 3.83 hours without Reclock after a couple of hours spent aiming for my 0.00246% clock deviation.

Why the heck isn't this info plastered all over the internet?

Glad I could help you The info is in the internet, but splitted on several sources...

Isn't that math wrong? If your refresh rate is too slow: 47.95204795, wouldn't the rate need to be larger not smaller (1 - 0.0026%) * 47.95204795 Hz = 47.9508012Hz. The video clock is now 0.0026% slower than the original

There is some misunderstanding regarding the clocks, I explained that already but I try again
In a computer different clocks are running. E.g. the audio clock and the video clock. They are running independently (if there would be ONE common clock, we wouldn´t have the described problem because there wouldn´t be a deviation then). You CAN´T change the speed of these clocks, they are simply running. They tick. Audio is being played back as multiples of the audio clock tick. Video is played back as multiples of the video clock tick. Once again: If the tick of the two clocks would be at the SAME rate (or whole number mutiples) then there would be no problem (why are there two clocks and not one clock you may ask: simple: the audio clock sits physically on the soundcard/integrated sound, the video clock sits on the videocard/integrated video, they are simpel quartzes)
Reference clock is the audio clock. So audio is always running fine. Now there is usually a mismatch between the video and the audio clock. Video is normally not speeded up or down on the fly, so what happens: Depending on the sign of the deviation frames are dropped or repeaten. We don´t like that.
So e.g. madvr can do some kind of video-onthefly-speedup/down called Smoothmotion (I don´t explain the mechanism here). If you don´t use madvr or don´t want to use Smoothmotion there is the possibility of custom resolutions.
Coming back to the quote: No. it is not the video clock that is now 0.0026% slower. The audio clock and the video clock are still running at their same former speed. By a custom resolution you change the multiple of the video clock (that´s not perfectly correct in this way but easier to understand). So for the given example: The duration of one frame with no clock mismatch would be 1 / refresh rate = 1 / 47.95204795 Hz = 20.8542 ms (rounded). Now let´s assume on clock tick durates 1ns (nanosecond). So we would have 20.8542ms / 1ns ticks = 20854167 ticks. But we have in our example a -0.0026% mismatch so we would like (1 / 47.9508012Hz) / 1ns = 20854709 ticks. Keep in mind: the negative sign of the given mismatch says: the frequency of the video clock is slower than the frequency of the audio clock. So for the refresh period it is reverse: we need longer refresh period. And that´s now in the numbers: 20854709-20854167 = 542. That´s now the difference: We need 542 multiples more of the video clock tick time to get perfect playback without drops or repeats.