Op 13-2-2011 15:28, Mark Robinson schreef: > On 14/02/11 00:28, Marco Langbroek wrote: >> Op 13-2-2011 02:24, Bill Arnold schreef: >> >>> This observation was timed with a digital watch that was calibrated with time.gov just before I went out to watch. The time was stated to be accurate to within 0.2 seconds. My watch was in sync with the time.gov page. The watch was calibrated again when I came back in from outside, after about 20 minutes, time remained the same. >> >> I would strongly advise against using webbased time services for time >> calibration. Even if the time server itself is correct, internal processes in >> your PC and your ISP's network introduce time lags. >> >> Time signals obtained over the internet *never* can be accurate. > > Nothing is ever completely accurate, however NTP manages to hold my machines > within a few ms. Unfortunately, variable protocols running on your PC and your operating system assigning variable priorities to different instances of software running on your pc, introduce variable delays *internally* in your pc in distributing time signals to software or your display. For this reason it is never wise to use the pc clock for accurate time keeping when you need subsecond accuracy. It is exactly for this reason that for example observers of asteroid occultations use a GPS time inserter that inserts the time-mark into the video stream *before* it enters the pc. Practical results show that otherwise the time-keeping is simply not reliable enough. My own PC adjusts its internal clock each 5 minutes (using Dimension4, not the native Windows thingy), yet I can often see clear discrepancies between the pc clock changing seconds on the screen compared to a DCF77 clock. - Marco _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-l
This archive was generated by hypermail 2b29 : Sun Feb 13 2011 - 15:57:24 UTC