I just built the Cat Tracker using the GPS tiny shield.  This morning I put it on the dash of my car as I drove to work and then uploaded the file to Google Earth.  The track appears to be consistently off by about 1/2 block from the streets that I drove on.  I have the GPS shield on the top of my stack and it was forward on the dash with a clear view of the sky.  Is this shield that inaccurate or did I do something wrong?