Hi Bill,

I think that there may be an error in the planetary data that is called
up by the "More info" button: What Guide reports as the sidereal period
in days appears, according to
http://nssdc.gsfc.nasa.gov/planetary/planetfact.html, to be the tropical
period, at least where Saturn and Jupiter are concerned (the only ones
that I've checked).
--
Stephen Tonkin