The Earth's rotation is not perfectly constant. It speeds up and slows down slightly over time, and this can affect our clocks. To keep our clocks in sync with the Earth's actual rotation, we occasionally need to add or subtract a "leap second."

Leap seconds are added when the Earth's rotation has slowed down enough that our clocks are running ahead of the actual time. They are subtracted when the Earth's rotation has sped up enough that our clocks are running behind.

The next leap second will be added on June 30, 2023, at 23:59:60 UTC (Coordinated Universal Time). This means that the day of June 30 will actually be one second longer than usual.

Leap seconds can cause problems for some electronic devices, such as computers and cell phones. This is because these devices often rely on a precise timekeeping system, and the addition of a leap second can cause them to malfunction.

To avoid these problems, most electronic devices are programmed to ignore leap seconds. This means that when the clock strikes 23:59:60 UTC on June 30, the time on most devices will immediately jump to 00:00:00 UTC on July 1.

However, some devices, such as atomic clocks, are not programmed to ignore leap seconds. This means that these devices will continue to run at the correct time even after the leap second is added.

If you are using an electronic device that is not programmed to ignore leap seconds, you may need to take special steps to ensure that it continues to work properly. For example, you may need to reboot your computer or cell phone after the leap second is added.

For more information about leap seconds, please visit the National Institute of Standards and Technology (NIST) website.