This is a result of a short baseline (about 3.7 km) in a low multipath environment, using two high quality C/A code/ carrier receivers.

The 'truth' has been established with carrier phase double diffenrence processing and is believed to be within a few mm's.

The blue line is difference in the height from single difference C/A code processing and the true height and contains about 2900 points. The red dots are 10 sec averages, the blue dots 100sec averages.

Some notes:

• The deviations from zero are believed to result from multipath only, S/A induced satellite position errors of 100 m (a conservative estimate) result in position errors of less than a few cm's at this baseline length, S/A induced satellite clock errors cancel because both receivers were well aligned to the GPS system time.
• The first 1500 seconds suggest effective averaging to within 1 m, while the last 1500 second contradict this suggestion ! This is a fine proof of how cautious one should be with the results of averaging, even in the differential mode.

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