on a PC: In OpenBSD 4.1 the nmea(4) line discipline can attach to a GPS timer and optionally use the PPS signal for low jitter and high accuracy in system time and NTP time gpsd — a GPS service daemon, required to activate PPS signal on some devices (works in conjunction with OpenBSD's nmea line discipline if installed via ports tree and a stand-alone service daemon for other operating systems) RFC 2783 Pulse-Per-Second API for UNIX-like Operating Systems, Version 1.0 PPS pulse and PPS pulse distribution Measurement Time