Leap Second 2005

A leap second was inserted into the last minute of 2005. This page contains some information recorded around the leap second.

Rugby Radio Signal

I have a Rugby Radio wired to the DCD pin on a serial port, so I can record if the signal is on or off. Each minute of the signal begins with a 0.5 second on/0.5 second off period. The following graph shows the beginning of each minute around the start of the year.

Graph of Rugby minute marker

Note that the minutes before the new year began 61, 121 and 181 seconds before the new year, indicating that the last minute had an extra second. The full minute of each signal can be seen here.

Graph of full minute Rugby signal

Note that the next minute marker is visible at the right hand side of the graph (at second 61) for all the signals but the third from the bottom. This is the minute with the extra second.

The raw data and postscript versions of these plots are also available. Information on the Rugby signal can be found on the UK's NPL web site, including information on how the signal is encoded.

NTP Leap Second Flags

NTP warns of impending leap seconds using two bits: 00 means no leap second, 01 means we are adding a leap second, 10 means we are removing a leap second and 11 means the server is unsynchronised.

The NTP project maintains a list of public time servers at stratum 1 and stratum 2. Some of these servers will respond when asked for the value of the leap bits. The following is a graph of the proportion of (responding) NTP servers with various values of the leap bits. The verticle line shows when the leap second should have been inserted.

Graph of proportion of servers with leapbits

The first 3 points are on the Dec 30th, and only a small proportion of servers had their leap bits set. There was a big jump up in the number of servers advertising the leap second 24 hours before it was due to happen, and another jump 1 hour before hand. Interestingly, in the hour immediately before the leap second, one server decided that a leap second should be removed!

Unfortunately I missed a measurement in the hour immediately after the leap second, but the proportion advertising the leap second is clearly decreasing. Interestingly, there are a handful of stratum 1 servers that have become unsynchronised after the leap second.

For reference, the number of servers responding was roughly constant throughout the measurements and is shown below.

Graph of responding servers

Log messages

Our Linux machines' kernels logged a message indication the insertion of a leap seconds.

Dec 31 23:59:59 turing kernel: Clock: inserting leap second 23:59:60 UTC
Dec 31 23:59:59 graham kernel: Clock: inserting leap second 23:59:60 UTC
Dec 31 23:59:59 ns1 kernel: Clock: inserting leap second 23:59:60 UTC

On a Tru64 box running xntpd the following was logged.

Jan  1 00:00:01 web1 xntpd[437]: leap second occurred, stepped time back 1 second

The load on our NTP server (in packets per minute) looked like this.

Load in PPM

The extra load starting about 10:00 is just extra monitoring we were doing. The extra load starting around 23:30 we're not sure about. The peak at midnight is something that we see most nights.

Either our GPS unit didn't output a RMC sentence for the leap second, or it was filtered out by some software between the serial port and my logging. Unfortunately I didn't timestamp the sentences, so I can't tell if it inserted a blank second. It was out of sync, so it may have done nothing.


Eircom Speaking Clock

A simple recording of the Eircom speaking clock, made using a MP3 recorder and a microphone held up to the phone. The speaking clock sends a marker every 10s for 0s, 10s, 20s, 30s, 40s, 50s in each minute. As far as I can tell, working with Audacity all these markers are 10s apart (at about XXmY6.8s from the start of the recording). Midnight is marked at about 2m56.8s. There doesn't seem to be a leap second inserted by the clock.

It also seems the beeps are about 1kHz and about 120ms long, which I never knew before.

NTP Peer Plots

There are some graphs of what a number of our NTP peers did, and a brief explaination of the sort of thing that we saw.