On 2011-09-15 21:55, Poul-Henning Kamp wrote:
Actually, the _really_ interesting thing is that they resort to using
a cos() function to herd the NTPD pll's in their system, but that
is more a testimony to how bogus that PLL code really is.
The correction term is (1 - cos(t))/2 = sin(t/2)^2,
hence Google's modification of UTC is four times
continuously differentiable.
The minimal rate is
d(TAI)*(1 - pi/2/(window length in seconds))
hence the slowdown is 57 % larger than with the
piecewise linear method (as used by Markus Kuhn's
SLS) over the same window. The piecewise linear
method gives a time scale that is continuous but
not differentiable.
Michael Deckers.
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