The difference is minute -- all of five millimeters -- but that is crucial to studying how climate changes the Earth, said researchers at Bonn University.

Five millimeters (0.2 inches) is less than half the width of an average finger, which may seem negligible in comparison to the earth's diameter of 7,926.3812 miles.

But "it is essential for the positioning of the satellites that can measure rises in sea level," said lead researcher Axel Nothnagel. "If the ground stations tracking the satellites are not accurate to the millimeter, then the satellites cannot be accurate, either."

Nothnagel's team worked for two years using radio waves to measure the Earth's diameter, Deutsche Welle reported Friday.