NTP is accurate within a few milliseconds. GPS is accurate within a few microseconds. However, you need to hook into the PPS (pulse per second) on the GPS signal to get proper accuracy. Think of it like a super-precise drummer keeping beat. NTP servers typically use GPS as a primary time source.
Source: I operate a stratum-1 time server in the NTP pool.
NTP is accurate within a few milliseconds. GPS is accurate within a few microseconds. However, you need to hook into the PPS (pulse per second) on the GPS signal to get proper accuracy. Think of it like a super-precise drummer keeping beat. NTP servers typically use GPS as a primary time source.
Source: I operate a stratum-1 time server in the NTP pool.