> In short, yes. If you want true traceability to NIST, you need to take > into account UTC(GPS) versus UTC(NIST).
And it gets uglier yet. If you want UTC you have to take into account the UTC - UTC(NIST) delta, which was about 16 ns in January. See the full 2006 record: http://tf.nist.gov/timefreq/pubs/bulletin/nistutc2006.htm The point is GPS, NIST, USNO often vary up to tens of ns over the span of days and months. It highlights the problem of knowing what the "true time" is. Also note that, strictly speaking, there is no such thing as "UTC(GPS)" and BIPM frowns on the phrase UTC(k) where k isn't one of the national time labs (e.g., NIST, USNO, NPL, PTB). What we call "GPS time" is in fact a good approximation to UTC(USNO) but since the official UTC(USNO) clock goes through so many levels of distribution, Kalman filters, uplinks, downlinks, 24+ individual SV clocks, and PLL'd disciplined oscillators before it reaches your 1 PPS BNC output, it is no longer "UTC(USNO)". For ns-level work the key is post-processing, where many of the systematic and variable offsets can be estimated days or months later and mathematically backed out from your archived physical time interval measurements. /tvb _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts