As I recall, the "60 Hz" vertical scan rate for NTSC is not supposed to be exactly 60 Hz, but slightly different, to provide color and still maintain integer counting values. Likewise, the horizontal is not 15,750 Hz as in monochrome, but something like 15,734. This was all part of the trick to squeeze the vector modulated color info into the spaces between the normal monochrome scan spectral lines, and magically work for both color and B&W TV sets, with "mostly" full compatibility, and without needing any extra channel bandwidth. If you study up on NTSC, you can get the exact values and rationale of the scheme. I've always found it quite fascinating how this was figured out and done way back when. I used to understand it, but it's been a lot of years.
Anyway, you can force your unit to run at exactly 60 Hz by tweaking the oscillator to match whatever divide ratio is used. The HP/Grass Valley thing likely wasn't intended to make exactly 60 Hz, but the NTSC version of it. Changing that to real 60 Hz would be a much bigger project.
Ed
