Jupiter moons is a great iOS app which draws from Sky & Telescope info. It is always accurate in my experience. Stellarium can be inaccurate for several reasons. Firstly, as mentioned already the spot drifts with respect to the meridian, and so there is a parameter an .ini file which needs correcting to get the timing right. There are details on the forum if you search. Secondly, the light transit time from Jupiter varies, normally it is 30 or 40 minutes. Stellarium has an option 'simulate light speed' which effectively delays the positions of moons and GRS by this time, making them accurate as we see them from earth rather than as they actually happen. Jupiter moons and the app on the S&T site correct for both these parameters so they are always correct. Stu Sent from my iPhone using Tapatalk