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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Time and cel nav, a stupid question
From: Lu Abel
Date: 2008 Apr 22, 18:45 -0700
From: Lu Abel
Date: 2008 Apr 22, 18:45 -0700
Wow! I guess I stand corrected on cellphones telling time. I live in the San Francisco area and work in high tech. Just polled a bunch of my friends who have AT&T service; they report that their phones are 3 to 5 seconds slow as compared to either time.gov or Unix NTP. AT&T now runs GSM (the cell phone scheme used in most of the world except the US), so I wonder about T-Mobil (the other major GSM vendor in the US). At the same time, I wish I knew more about GSM so I could understand how it sends time to phones. 50 seconds slow sounds like a LOT! Lu Fred Hebard wrote: > On a mac, using time.apple.com. Just synced, and still about 50 > seconds slow. > > On Apr 22, 2008, at 6:12 PM, Lu Abel wrote: > > >> Fred: >> >> I'm not an expert on cell phone technologies, but it may be that >> AT&T is >> the one provider that may not need accurate timekeeping to make its >> particular technology work. >> >> When you say you're on a network time server, are you on a Windows, >> Mac >> or Unix machine? Windows only resynchronizes the computer's >> time-of-day clock with an NTP server once a week (or even less >> frequently); I've seen at least one of my computers drift >> considerably >> in between. I just checked my new Vista PC computer's clock against >> time.gov, it's three seconds slow with a resynchronization >> scheduled for >> Friday. But it could just as easily be fast, as yours might be. I >> personally have a lot of faith in time.gov (especially with a >> broadband >> connection) because it attempts to measure and compensate for any >> network delay. >> >> Wait, I forgot that I also have one of those digital clocks that >> synchronizes itself to the low-frequency time signal broadcast by >> WWVB. >> It appears to be between 0.3 and 0.5 seconds slow as compared to the >> www.time.gov display on my computer. On the other hand, considering >> that it cost me all of $6, I have to wonder whether its time >> display is >> more or less accurate. >> >> Lu >> >> Fred Hebard wrote: >> >>> I followed up on this when it was mentioned previously on this list, >>> and I believe the accuracy of cell phones may vary with the network. >>> I'm on AT&T, and my impression is that the time is not accurate. For >>> instance, my phone now says it's 9:51:55 and my computer says it's >>> 12:52:42. The computer is getting its time from a network time >>> server. These may be more accurate than the USNO site, but, I don't >>> know this one way or another. >>> >>> Fred Hebard >>> >>> On Apr 22, 2008, at 11:56 AM, Lu Abel wrote: >>> >>> >>> >>>> Bill: >>>> >>>> The time difference between your Garmin and the USNO web site is >>>> likely >>>> due to network delays (ie, the USNO sends you a time pulse at the >>>> correct time, but it takes almost a second to arrive at your >>>> computer). The other web site run by USNO, www.time.gov, says it >>>> attempts to measure network delays and compensate for them. >>>> Another >>>> source for accurate time is your cell phone. Mine only keeps >>>> time to >>>> the minute, but it very accurately rolls over at the 60-second mark. >>>> >>>> Lu Abel >>>> >>>> Bill wrote: >>>> >>>> >>>>> The current discussion on time, relativity and leap seconds is, in >>>>> many >>>>> areas, well above my head. Noting the various flavors of UT >>>>> (currently), an >>>>> observation and a pragmatic question for cel nav. >>>>> >>>>> The seconds readout between my GPS (Garmin GPS 76) and >>>>> http://tycho.usno.navy.mil/cgi-bin/anim >>>>> differ by about one (1) second. >>>>> >>>>> The web site (dial up modem at the moment) is nominally one (1) >>>>> second >>>>> behind the GPS readout. >>>>> >>>>> Bringing it into the realm of traditional navigation, which time >>>>> do I use to >>>>> set my hack watch? ;-) Potentially a quarter mile intercept >>>>> difference >>>>> under ideal circumstances. >>>>> >>>>> I do not have access to a time-signal radio now. >>>>> >>>>> Bill >>>>> >>>>> >>>>> >>>>> >>> >>> > > > > > > --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---
