Why this is a real NTP query, not a ping with a clock reading

Reading an accurate time offset requires the actual NTP exchange — sending a request and receiving a response, each timestamped, and using all four timestamps (request sent, request received by the server, response sent, response received) to compute both the offset and the round-trip delay separately. That's meaningfully different from just asking a server "what time is it," because a naive single-timestamp exchange can't distinguish "the clocks differ" from "the network is slow" — both would show up as the same apparent time difference. NTP's four-timestamp exchange is specifically designed to separate those two effects, which is why this tool speaks the actual protocol on UDP port 123 rather than approximating it with a simpler request.

What stratum actually measures

Stratum describes distance from an authoritative time reference, not accuracy in some abstract sense — stratum 1 servers are directly attached to a hardware reference clock (GPS receiver, atomic clock, radio time signal), stratum 2 servers sync from a stratum 1 server, stratum 3 from a stratum 2, and so on, with each hop away from the reference adding a small amount of potential drift and network latency. A stratum 1 server's reference ID field identifies which physical clock source it's reading from (a 4-character code like "GPS "), while a stratum 2+ server's reference ID is simply the IP address of whichever upstream server it's currently syncing from — which is why this tool displays that field differently depending on the reported stratum.