The author states:

>"The mean time recorded there was used as the one to derive your local civil time as an offset from, called Greenwich Mean Time, or GMT for short. However, it was not as precise as it could be and thus got replaced in 1967 by another standard called Universal Coordinated Time, UTC.

UTC is a version of the Universal Time standard. In this standard we also find UT1, that keeps track of Earth rotation angle using GPS satellites ..."

I was confused by this as my understanding is that the first GPS blocks were the NAVSTAR system which were launched in 1978[1]. Or am I reading this incorrectly and UT1 is a later version of the UTC standard?

[1] https://www.nasa.gov/directorates/heo/scan/communications/po...