This read-only Unsigned32 (1-255) is the PRN (pseudo-random noise) number identifying a specific satellite currently tracked by the device's GNSS receiver. An administrator uses it to know exactly which satellite each row of tracking data corresponds to, which is essential when correlating signal quality or azimuth entries to real, identifiable space vehicles. For example, seeing SV number 21 in this table lets a technician look up that specific GPS satellite when investigating a timing anomaly.