Whence 556?

[Christian Corti]

On Sat, 2 Jun 2018, Chuck Guzis wrote:
> So 200 and 800 are nice decimal multiples of 10.   But 556 doesn't fit
> that pattern--it's not a "nice' number, being the product of 4 and 139
> and doesn't correspond to any computer-related characteristics that I
> know of. It's not metric.  So why 556 and not 400, 512 or 600?

Just a guess, but 556 kHz is 5 MHz divided by 9.

Christian