QUOTE:

GPS Time is the time standard of the GPS system. It is also known as GPS
System Time (GPST). Coordinated Universal Time is the time standard for
the world. The rates of these two standards are virtually the same.

Specifically, the rate of GPS Time is kept within 1 microsecond, and usually
less than 25 nanoseconds, of the rate of Coordinated Universal Time (UTC).

The exact difference is in two constants, A0 and A1 in the NAV message, which give the time difference and rate of system time against UTC.

The rate of UTC itself is carefully determined. It is steered by about 65 timing laboratories and hundreds of atomic clocks around the world and is remarkable in its stability. In fact, it is more stable than the rotation of the earth itself, such that UTC and the rotation gradually get out of sync with one another.

However, leap seconds are not used in GPS Time. It is a continuous timescale. Nevertheless, there was a moment when GPS Time was identical to UTC. It was midnight, January 6, 1980. Since then, many leap seconds have been added to UTC, but none have been added to GPS Time.

So, even though their rates are virtually identical, the numbers expressing a particular instant in GPS Time are different by some seconds from the numbers expressing the same instant in UTC. For example, GPS time was 16 seconds ahead of UTC on July 1, 2012 and 18 seconds ahead of UTC on September 11, 2020.

Information in subframe 4 of the NAV message includes the relationship between GPS time and UTC, and it also notes future scheduled leap seconds. In this area, subframe 4 can accommodate 8 bits, 255 leap seconds, which should suffice until about 2330.

On Thursday, March 9, 2023 at 9:39:45 PM UTC-3, Richard Hertz wrote:
> QUOTE:
>
> GPS Time is the time standard of the GPS system. It is also known as GPS
> System Time (GPST). Coordinated Universal Time is the time standard for
> the world. The rates of these two standards are virtually the same.
>
> Specifically, the rate of GPS Time is kept within 1 microsecond, and usually
> less than 25 nanoseconds, of the rate of Coordinated Universal Time (UTC)..
>
> The exact difference is in two constants, A0 and A1 in the NAV message, which give the time difference and rate of system time against UTC.
>
> The rate of UTC itself is carefully determined. It is steered by about 65 timing laboratories and hundreds of atomic clocks around the world and is remarkable in its stability. In fact, it is more stable than the rotation of the earth itself, such that UTC and the rotation gradually get out of sync with one another.
>
> However, leap seconds are not used in GPS Time. It is a continuous timescale. Nevertheless, there was a moment when GPS Time was identical to UTC. It was midnight, January 6, 1980. Since then, many leap seconds have been added to UTC, but none have been added to GPS Time.
>
> So, even though their rates are virtually identical, the numbers expressing a particular instant in GPS Time are different by some seconds from the numbers expressing the same instant in UTC. For example, GPS time was 16 seconds ahead of UTC on July 1, 2012 and 18 seconds ahead of UTC on September 11, 2020.
>
>
>
>
> Information in subframe 4 of the NAV message includes the relationship between GPS time and UTC, and it also notes future scheduled leap seconds. In this area, subframe 4 can accommodate 8 bits, 255 leap seconds, which should suffice until about 2330.

Updated every 12 minutes, as digital words, to every GPS receiver in the entire world. Satellite time downloaded without "corrections".