1. Related Links
Because NTP is a widely-used an well-established service, people who write tools for system administrators frequently have features and plugins designed to help you work with it. This page collects some references that may be useful.
The Wireshark protocol analyzer has support for displaying NTP packets with the fields broken out and interpreted.
The Nagios monitoring suite has native support for querying NTP servers. The check_ntp_peer and check_ntp_time programs may be of particular interest.