[time-nuts] sub-minute time-precision in court-case

[Tim Shoppa]

You can find (for better or worse) NTSB analysis of various recorder
timestamps relative to "cell phone timestamp".

http://www.ntsb.gov/investigations/summary/RAR1001.html

6
 In this report, all times associated with the sending or receiving of
calls and text messages are from Verizon
records. In these records, the “sent” and “received” times are based on a
GPS time reference and reflect the time the
Verizon Wireless network equipment either receives or delivers a message.
Thus, the reported “sent” time of a
message does not necessarily correlate to the time the sender pressed the
“send” button on the wireless device.
Because the network must query the receiving device to make sure it is
available before transmitting a message, the
“received” time is more likely to reflect the actual time the message
arrives on the recipient’s device.
7
 In this report, all times associated with signal, switch, and locomotive
events are based on signal log and
locomotive event recorder data synchronized to a GPS reference time. This
synchronization correlates train position,
data recorder, signal, and cell phone send/receive times to a common
“master clock” that reflects actual GPS time.


On Tue, Sep 3, 2013 at 1:48 PM, Alan Melia <alan.melia at btinternet.com>wrote:

> I remember a lecture by an officer of the (London) Met Police about how
> tracable time was essential to demolishing the defence of "wrong clock"  in
> accidents involving the illegal use of mobile phones when moving and even
> parking meter tickets. They had to argue why the cell time was "more right"
> than the defendants watch!! This was part of a meeting of the Time and
> Frequency Club at the NPL at Teddington about 6 years ago.
>
> Alan
> G3NYK
>
> ..
> ----- Original Message ----- From: "Mike S" <mikes at flatsurface.com>
> To: <time-nuts at febo.com>
> Sent: Tuesday, September 03, 2013 5:19 PM
> Subject: Re: [time-nuts] sub-minute time-precision in court-case
>
>
>
>  On 9/3/2013 10:56 AM, Jim Lux wrote:
>>
>>  In this case, all the messages were presumably handled by the same
>>> carrier, so the issue of skew in timestamps is negligible; they're all
>>> presumably running off the same clock.
>>>
>>
>> But not necessarily the same time. For instance, some cell systems run on
>> GPS time, but the carrier may keep records in UTC, since it's the legal
>> time in most jurisdictions. A phone might time stamp using either (Google
>> has a years-old bug in Android which lets it use GPS time and not UTC). So,
>> different devices on the same network may not be in sync.
>>
>>
>>
>> ______________________________**_________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/**
>> mailman/listinfo/time-nuts<https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts>
>> and follow the instructions there.
>>
>
> ______________________________**_________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/**
> mailman/listinfo/time-nuts<https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts>
> and follow the instructions there.
>