On 3/9/2011 12:11 PM, Darren New wrote:
> Le_Forgeron wrote:
>> Civil usage of GPS is accurate to 30 yards/meters.
>
> I think they turned off the encryption of the low bits back in Clinton's
> timeframe, when other countries started threatening to launch their own
> satellites. I think civilian GPS is quite accurate now.
>
> Especially if you're measuring something that isn't moving, and you can
> let the device sit for a day, you can get down in the milimeter range.
>

Atmospheric drift still plays a factor.  You can reference to a known 
nearby location that is receiving GPS signals to help nullify the effect 
as the 'location' will drift as well.

take a look at Wide Area Augmentation System

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