Which grade of Stratum represents a primary time server?

The grade of Stratum 1 represents a primary time server. This means it is directly connected to a reference clock source, such as a GPS or atomic clock, which provides highly accurate time information. Stratum 1 servers are considered the most accurate and reliable sources of time within the hierarchical network of time servers. Other Stratum levels, such as Stratum 2 or higher, derive their time from Stratum 1 servers, making them less direct and potentially introducing some levels of variance in accuracy. Consequently, Stratum 1 serves as the foundation upon which other time servers synchronize, ensuring that they all maintain a consistent and accurate time standard.