[time-nuts] Position accuracy to improve Thunderbolt performance

[WarrenS]

Does anyone know how accurate Google map is for Lat & Lon in California?
I can see my GPS antenna & measure it's position to within about 1 ft on their Map. 
Any reason to believe that is more accurate than the Tbolt survey, which shows a 1 Ft by 3 Ft difference?

Can anyone tell me how I can get a better height reading, or improve & verify the Tbolt survey number which seems to vary as much as 10 ft each time.

warren