Another technique used in the study measured the distance between Earth and various satellites in the sky.
Overall the study used 400 observation sites and compiled data taken between 1984 and 2005. Analyzing all the data and carrying out the calculations took two years.
So why do these tiny movements matter, and do we really need to know Earth's size to the nearest millimeter? The answer is probably yes, if you live on a sinking continent.
"[The measurement] provides us with access to a coordination system against which we can measure environmental change," said Marek Ziebart, a mathematician at University College London who wasn't involved in the study.
If ice caps continue to melt or water begins to evaporate from the Amazon Basin, these new exact measurements will enable scientists to more accurately track the effects, Ziebart explained.
(See an interactive map of the effects of global warming.)
"If you have a tide gauge telling you that the sea level is rising, how do you know that it is not the continent which is subsiding [or sinking]?" Nothnagel said.
For scientists who want to determine whether the sea level has risen by just a millimeter a year, the measurements on the ground have to be just as precise, he said.
The new measurements also allow scientists to monitor continuing trends that have been spotted in previous surveys, the research team noted.
North America and Europe continue their steady parting of ways, as the Atlantic Ocean grows wider due to the process of continental drift.
Meanwhile, northernmost sections of Europe and North America keep gaining in elevation, as they buoy up after the huge weight of ice was lifted at the end of the last ice age.
"Canada and Scandinavia are responding to post-glacial rebound," Nothnagel said.
He and his colleagues are now gathering data for the next mammoth calculation effort, which is due to begin in 2008.
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