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To NTP or not to NTP

So here's an odd thing. I mentioned a few journal items ago that I wanted to get a watch that automatically sets its time via the radio signal from Ft. Collins, CO. With the Gramma Cash(TM), I bought myself the "Casio Atomic Shock Tough Solar watch":http://www.casio.com/index.cfm?fuseaction=products.detail&Product=GW300A%2D1V that fills this requirement. Other than the fact that it relies on light to recharge its batteries, I think it's cool. It definitely sets it time every day -- I can see that it almost always has a high "time signal strength" level. It's a little bigger than my old watch (height-wise), but I'm adjusting. We'll see how it goes. I was bored tonight, and on a whim, I compared the watch's time to the digital clock on my Verizon cell phone. My cell phone doesn't have a seconds display, but hypothetically, they should change the minutes value at more-or-less exactly the same time (as far as the eye can tell, anyway). Shockingly enough -- they don't. My cell phone changes the minutes value almost a full second before my watch. This is really weird -- both should hypothetically be within milliseconds of "real time" because both are frequently synchronized with a central source (the watch supposedly re-syncs at least 4 times a day). I suppose there can be multiple sources of error here: * simple lack of precision (i.e., precision granularity on the order of, say, tens or hundreds of milliseconds) on either device * the cell phone time is sufficiently far down from a true NTP source that it is actually hundreds of milliseconds off * the cell phone only synchronizes once in a long time, and when I saw it noticably different than the way, it had just drifted a lot * the martians are pissed off about us sending annoying probes to their planet and have decided to retalliate by skewing all of our clocks by infinitessimal ammounts, thereby raising the Earth's Geek Ire Level * propagation of the radio signal from Colorado to my location I'm guessing that the last one (radio propagation) is probably the most likely -- the cell phone syncs to a local tower, and the signal distance isn't nearly as far. The watch has no concept of its distance from the signal source, and I'm guessing that there's no negotiation (a la NTP) for it to be able to calculate its time-to-travel from the source. Hence, I'm guessing that if I was in the immediate vicinity of Ft. Collins, Colorado, the time on my watch and my cell phone would be virtually identical. It's still odd, though. :-)


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Comments (1)



I believe CDMA requires 10 usec precision in order to even function properly (implying that actual precision is much greater in the standard case). I’d venture that display update is just a low priority thread (especially when the phone is in low-power standby mode)

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