Greetings, Just a note -- in revision 719 -- I've committed a fix for the GUI component (reason) that was causing huge and inappropriate delays to projecting a dataset, if that dataset had more than about 10,000 grids. The GUI was updating every time a new grid was masked and examined, which was oftentimes many times more than once per second. It should be working now. Fixes have been committed to both trunk/ and branches/yt-1.0 . -Matt