[ntp:questions] Accuracy of NTP - Advice Needed

jimp at specsol.spam.sux.com jimp at specsol.spam.sux.com
Wed Dec 28 17:20:35 UTC 2011


Danny Mayer <mayer at ntp.org> wrote:
> On 12/28/2011 12:09 AM, jimp at specsol.spam.sux.com wrote:
>> Danny Mayer <mayer at ntp.org> wrote:
>>> On 12/27/2011 8:48 PM, jimp at specsol.spam.sux.com wrote:
>>>> Danny Mayer <mayer at ntp.org> wrote:
>>>>> On 12/24/2011 8:10 PM, jimp at specsol.spam.sux.com wrote:
>>>>>> John Hasler <jhasler at newsguy.com> wrote:
>>>>>>>> The open sky nearest the OPERA detector is straight up through 1400m of
>>>>>>>> rock.
>>>>>>>
>>>>>>> Jim Pennino writes:
>>>>>>>> And the easiest open sky to get to is horizontally down the tunnel to
>>>>>>>> the entrance which is next to a freeway.
>>>>>>>
>>>>>>> Yes, the entrance is next to a freeway.  The entrance to the LNGS
>>>>>>> facility where the OPERA detector is located is near the middle of the
>>>>>>> 10 km long Gran Sasso highway tunnel.
>>>>>>
>>>>>> The bottom line is that the only thing that is relevant is how easy it is
>>>>>> to get to a GPS antenna with an open view of the sky.
>>>>>>
>>>>>> Everything else is bloviation.
>>>>>
>>>>> GPS is not used for this kind of thing, they are too inaccurate, so it
>>>>> doesn't matter. They use atomic clocks.
>>>>>
>>>>> Danny
>>>>
>>>> How do you measure distance with an atomic clock?
>>>>
>>>>
>>>
>>> That's a complex question. GPS (even the military version) is not
>>> accurate enough.
>>>
>>> Danny
>> 
>> No, it is not complex; you can't measure distance with an atomic clock.
>> 
>> An atomic clock is used to measure time intervals.
>> 
>> As for GPS, it is pretty trivial these days to determine an absolute location
>> to parts of a centimeter for a fixed location.
>> 
> 
> There's no such thing as an absolute location. See Einstein.
> 
> Danny

Absolute within the frame of reference of GPS, which in case you didn't
know, is the Earth.

See Spot run.



-- 
Jim Pennino

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