Raspberry Pi NTP config with fudge factors

[Eric S. Raymond]

Frank Nicholas <frank at nicholasfamilycentral.com>:
> This is the “/etc/ntp.conf” I used when I ran my NTP server on a Raspberry Pi with the Adafruit breakout board (same as current hat).  I list it because of the “fudge” line.  This was commonly accepted as the proper fudge settings, especially for time2 - 0.350:

How do we know this will be correct for the HAT? Is that fudge really
associated with the MTK3339 itself, independent of surrounding hardware? 

> server tock.usshc.com iburst
> server clock.isc.org iburst
> server tick.apple.com iburst

What is special about these servers?
-- 
		<a href="http://www.catb.org/~esr/">Eric S. Raymond</a>