I had an idea that perhaps we could ignore the invalid GPS readings by observing whether there was a simultaneous jump in altitude. However, in one of the big spikes from yesterday the altitude readings are flat while the latitude and longitude values jump. It is interesting that the big jumps in longitude have all been positive in my graphs while the simultaneous latitude change is sometimes positive and sometimes negative. It would be nice to know whether these anomalies are specific to the Tesla Roadster's GPS receiver. What kind of antenna is needed to operate the GPS receiver in the modem? Maybe it would be possible to record data from both of the at the same time and compare. -- Steve