NTP uses A.B.C - style release numbers. The third (C) part of the version number can be: 0-69 for releases on the A.B.C series. 70-79 for alpha releases of the A.B+1.0 series. 80+ for beta releases of the A.B+1.0 series. At the moment: A is 4, for ntp V4. B is the minor release number. C is the patch/bugfix number, and may have extra cruft in it. Any extra cruft in the C portion of the number indicates an "interim" release. Interim releases almost always have a C portion consisting of a number followed by an increasing letter, optionally followed by -rcX, where X is an increasing number. The -rcX indicates a "release candidate". Here are some recent versions numbers as an example: 4.1.0 A production release (from the ntp-stable repository) 4.1.0b-rc1 A release candidate for 4.1.1 (from the ntp-stable repo) 4.1.71 An alpha release of 4.2.0, from the ntp-dev repo Note that after the ntp-dev repo produces a production release it will be copied into the ntp-stable and the cycle will repeat. The goal of this scheme is to produce version numbers that collate "properly" with the output of the "ls" command. Feel free to suggest improvements...