[LEAPSECS] Negative TAI-UTC

[Warner Losh]

On Sat, Feb 4, 2017 at 9:41 AM, Clive D.W. Feather <clive at davros.org> wrote:
> Looking only into the future, not historical data, what do people think the
> probability is that TAI-UTC will ever be negative? Should data structures
> be designed to handle this case or not bother?

Doubtful, but not impossible.

LoD would have to increase significantly for that to happen. The
current LoD delta is about 1ms. This looks to vary between -500us to
2ms on IERS' web page (http://hpiers.obspm.fr/eop-pc/index.php).  It
also looks like the short term forecast is to return towards 0 in the
next 150 days or so. Looking at even longer term data from
http://www.usno.navy.mil/USNO/earth-orientation/eo-products/long-term
we see huge error bars for LoD just a few hundred years ago and a big
drop in deltaT from 1850-1900. So the data we have suggests that it is
unlikely, but not outside the realm of possibility.

It's quite likely that the first negative leap second would have a
much higher bug rate than the current positive leap code which has at
least been tested several times and is known to still have issues.

Warner