The brief quote in the article has left the wrong impression, I think. I don't think the goal is to get a precise value of an arbitrary metric as an end in its

The brief quote in the article has left the wrong impression, I think. I don't think the goal is to get a precise value of an arbitrary metric as an end in itself. I think the science here is that there is (1) an optically measurable (latitude-dependent) rotation rate of top-of-atmopshere gas; (2) a magnetically measurable rotation rate (and axis) of subsurface conductive hydrogen; and (3) gravimetrically measurable rotation and density. The close approaches of Cassini to Saturn will allow much better gravimetric measurements. It's surprising what can be pulled out of gravimetric techniques, see, e.g., https://www.jpl.nasa.gov/missions/gravity-recovery-and-climate-experiment-grace/ https://www.jpl.nasa.gov/missions/gravity-recovery-and-clima.... They would like to compare these measurements to get insight about the interior composition of the planet. For a bit more, see this old overview: https://futurism.com/new-spin-saturns-rotational-period/ https://futurism.com/new-spin-saturns-rotational-period/ and http://www.nature.com/nature/journal/v460/n7255/full/460582a.html http://www.nature.com/nature/journal/v460/n7255/full/460582a... * It may be surprising, but groups have been working on general circulation models (GCM) for outer planet atmospheres for over a decade, and the state of the art is pretty advanced. (A good recent presentation with lots of nice plots: https://theoryofclimate.sciencesconf.org/conference/theoryofclimate/Slides_Spiga.pdf https://theoryofclimate.sciencesconf.org/conference/theoryof...) The top-of-atmosphere rotational velocities would be a major constraint on models like these.