Could someone provide an introduction to how the rates of these
reference clocks are adjusted? What's going on inside the black box?

For instance, I once tweaked the rate of a cheap sports watch by
opening it up and turning a screw that applied force on the crystal
physically altering its frequency. I'm sure this is not how these NTP
reference clocks are adjusted.

Can the frequency of the crystal (or whatever) oscillators be adjusted
by applying some bias voltage?

Or are oscillations counted and the rules for issueing 1-second
signals adjusted. A count of oscillations will be an integer so
every N seconds a 'leap oscillation' is allowed in the count for
higher precision? and for a rate adjustment?

Or is the phase of the oscillations tracked so precision finer than
the oscillator period is directly achievable?

I'm just making wild guesses here.

Or do the higher level NTP servers use their own local atomic clocks
and not quartz crystal based clocks?

Richard Clark

On Thu, 1 Dec 2016, Brooks Harris wrote:

Hi Stephen,
On 2016-12-01 02:49 AM, Stephen Colebourne wrote:
More details on the developer site:

Notably this page:

which include "Our proposed standard smear" - "We would like to
propose to the community, as the best practice for leap seconds in the
future, a 24-hour linear smear from noon to noon UTC"

Hip hip hooray! De facto standards for the win!

Ah, this is good. I'd missed that page yesterday.

I might suggest you good go a little further.

You say "Each second of time marked by Google's servers will be about 13.9 μs longer than an SI second. "

Some developers may probably need to know exactly, or as exactly as possible, the ratio.

If I've got this right:

20 hours = 20 * 60 * 60 = 72000 seconds
Plus the Leap Second = 72001 second
So the ratio is 72001 / 72000 = 1.000013889 (rounded to 10-9th precision, nanoseconds)
This a repeating decimal number which may be denoted 1.000013(8).
Applications should be careful to provide adequate precision for the purpose.


On 30 November 2016 at 21:05, Tom Van Baak <> wrote:
I'm surprised no one has posted this news yet:

"Making every (leap) second count with our new public NTP servers"


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