# [ntp:questions] Leap second to be introduced in June

Mike S mikes at flatsurface.com
Thu Jan 22 17:27:08 UTC 2015

```On 1/22/2015 5:45 AM, David Malone wrote:
> That assumes that UTC can be represented as a real number with the
> standard topology, which doesn't seem to be what TF.460 says. It
> describes each second as labelled, which means that you have to
> stitch together all possible unit intervals for each second with
> some topology, and then you can ask if the path taken by UTC through
> this space is continuous.

Both TAI and UTC are continuous, and could in a non-standard way, be
represented by real numbers ("Time," below), where they wouldn't differ.
TAI and UTC only differ in how they're "labelled," as you say. It's
POSIX which isn't monotonic or continuous, it repeats leap seconds. How
they handle leap seconds:

Time   UTC         TAI         POSIX
n+0    23:59:58    00:00:33    n+0
n+1    23:59:59    00:00:34    n+1
n+2    23:59:60    00:00:35    n+2
n+2.9  23:59:60.9  00:00:35.9  n+2.9
n+3    00:00:00    00:00:36    n+2
n+3.9  00:00:00.9  00:00:36.9  n+2.9
n+4    00:00:01    00:00:37    n+3

```