JoeN:
How accurate does a crystal have to be to generate a correct signal for VGA? I have done this project:FPGA VGA Resistor DAC - Introduction | PyroElectro - News, Projects & Tutorials
And it works just fine but some of the color banding is a little off and I was wondering if it could be timing. My crystal oscillator is counting at 25.17447Mhz which is pretty darn close to 25.175 but as the crystal says 25.1750 on it I am thinking doesn't that extra zero imply a significant digit there, i.e. that it should register between 25.17495 and 25.17505Mhz? Using that high standard, 25.17447Mhz is out of spec. But it still feels as if it's close enough that it shouldn't matter. What do you think?
Oh, and this counter is cheap but it seems to be accurate. I have two of the used 10Mhz rubidium standards off of eBay and when I count those, they count close but not right at 10.00000Mhz prior to lock but once they lock the counter shows them exactly at 10.00000Mhz which implies to me that this counter is actually very accurate (though cheap and it doesn't actually have an input to use those standards as a timebase which sucks).
The standards:
http://www.ebay.com/itm/FE-5680A-Rubidium-Atomic-Frequency-Standard-10MHz-out-/280655233263
The cheap counter:
25.17495 / 25.17505 = 0.999996
I would call that "close enough". It's only 100 HERTZ off!
Most crystals are not even manufactured that close.