The results of a VLBI global solution can depend on a great number of factors, including which observing sessions are used and how they were analyzed, the relative weights that stations are given based on how much data they contribute, the way that tides are modeled and earthquakes that shift station positions are treated, and many others.
Below are comparisons of the most recent USNO quarterly VLBI global solution with other solutions, including the C04, Bulletin A, and the previous USNO quarterly. Each comparison shows the differences in the values of the five Earth Orientation Parameters between the two solutions over time. Some scatter in the individual colored data points is expected, due to the variations in processing mentioned above - the overall trends in the time series are useful diagnostics of the differences. The time series tick marks denote days from January 1, 2000, with corresponding calendar year tick marks given at the top.
Comparisons of the current USNO global solution with the IERS C04 time series:
Comparisons of the current USNO global solution with the Bulletin A time series:
Comparisons of the current USNO global solution with the previous USNO global solution: