NavList:
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: Fred Hebard
Date: 2008 Apr 22, 18:26 -0400
From: Fred Hebard
Date: 2008 Apr 22, 18:26 -0400
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 -~----------~----~----~----~------~----~------~--~---