F-ckin Leap Seconds, how do they work?

Peter Lothberg roll at Stupi.SE
Tue Jul 3 22:18:24 UTC 2012

```> > > The system clock needs to be UTC, not UTC =C2=B1 some offset stuck
> > > somewhere that keeps some form of running tally of the current leap
> > > second offset since the epoch.
>
> > Nope.  UTC *includes* leap seconds already.  It's UT1 that does not.
>
> > Are you suggesting that NTP timekeeping should be based on UT1?
>
> The system clock should be based on UT1 and should be monotonically increas=
> ing since this matches the common concept of time.  Calculations done with =
> this value are all based on it being UT1 and using the "common" notion of U=
> T1 rules.  The root cause of the difficulties is that someone decided that =
> the system clock would not maintain "wall clock" time (UT1) but rather some=
>  other timebase and then "step" that time to keep it in sync with UT1.
>
> NTP can keep time in UTC (or anything else) if it wants, but it should disc=
> ipline the system clock to monotonically increasing UT1.

UTC is the universal time. UT1 is "astronomical time".

As the definition of a atomic second is 9192631770 complete
oscillations of cesium 133 between enery level 3 and 4, "everyone" can
make a second in their lab, that's TAI. Just add the lepsecond ofset
and you have UTC.

UT1-UTC is done by observations from radio astronomers VLBI telecopes
and a comitee, you can't make one in your lab, and it's not real
time.

--P

(The only SI metric you can't make is a kilogram, you have to have one
of the 28 kilos in the world..)

```