What is a Leap Second and How Does It Affect Me?

A leap second is a discontinuity in the world’s official timescale and is a risk for those:

  • Developing and maintaining GPS applications, and/or
  • Managing a precise network synchronization deployment

The last leap second occurred on December 31, 2016.

Let us help you understand your risk for the leap second vulnerability.

Clock Icon

This Essential Education topic is to assist you in understanding the leap second vulnerability, planning for the next leap second, to help ensure your applications will operate smoothly through the leap second event. A recent decision will keep the leap second around until at least 2023.

What is a Leap Second?

Since the official definition of time is based on atomic standards, a leap second is inserted in the UTC time scale to keep it in step with the solar day much like a leap day is used to keep the calendar in step with the seasons. A leap second can be added or removed. It typically occurs at the end of the day on December 31 or June 30 and usually announced approximately 6 months in advance.

How a Leap Second Effects GPS

You probably know that time synchronization is fundamental to how GPS works. The developers of GPS knew the system could not tolerate a discontinuity so GPS time is not affected by the leap second. But since GPS is ubiquitously used for time transfer, the GPS message includes leap second information that all GPS devices need to decode and properly handle. Spectracom simulators can test GPS devices compliance to the GPS interface specification for proper leap second handling and identify any detrimental effects of the leap second on the application. It also has the ability to perform similar testing on leap second handling in other GNSS systems.

How a Leap Second Effects Network Synchronization

Most time synchronization messages transmit time-of-day information in UTC, the official timescale that includes leap seconds. The most popular network time synchronization protocols, NTP and PTP, have a mechanism to alert a leap second is pending but it is up to the computer operating system to manage it properly. We have prepared a short video to help understand the issue of leap second handling in high precision computing applications.

Products Related to Leap Second

Spectracom time synchronization systems are fully compliant to best practices for leap second handling. The SecureSync system can even be used in a leap second test mode. For testing the capability of GPS devices and systems to manage the leap second, any GSG series GPS simulator can perform the most realistic test to identify any potential problem in advance of a leap second event.

Leap Second Resources