Len Over 21 wrote:

...
NTSC color subcarrier is exactly 3.579545454545454545454545....
MHz. :-)

With the correct integer divisor and correct integer multiplier, it
comes out to 500 KHz fairly exact.

"Fairly exact"? What's that mean?

Any repeating decimal can be written as a rational number, a/b.
That particular decimal above is exactly 315/88: Set that decimal
equal to N. Since two digits repeat, multiply both sides of the
equation by 10^2; we now have: 100N = 357.9545454... Next, subtract
the first equation from this second one; all the repeating 54 pairs
cancel due to this subtraction, giving us 99N = 354.375, a
terminating decimal. To eliminate the decimal point, multiply
both sides by 1000: 99000N = 354375. Now divide both sides by
99000: N = 354375/99000. This fraction simplifies to N = 315/88.
Hence, that original repeating decimal, 3.579545454... is exactly
equal to 315/88.

Note that if you have a repeating decimal with 3 repeating digits,
you'd multiple both sides of the initial equation by 10^3, etc.

Jeff KH6O
--
Chief Petty Officer, U.S. Coast Guard
Mathematics Lecturer, University of Hawaii System