In this paper we discuss the problem of obtaining precise measurements of end-to-end delay that are consistent over a long time period (hours to days). Such measurements are used by applications such as immersive virtual reality in order to maintain synchronization between multiple media streams over the lifetime of a session. Previous work has dealt with detecting and removing the impact of large step changes in endpoint clocks that occur when using NTPv2 and earlier. The more recent versions of NTP that are part of current Unix distributions correct clocks in a smooth, controlled fashion and so require us to develop a new method for obtaining precise long-term measurements. We present a method that uses one of the statistics reported by NTP to improve estimates of one-way delay. We also show how to estimate the variance in delay estimates using another NTP statistic. Our results were obtained from measurement studies in a captive multi-hop network using a precise, standards-traceable reference clock
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