You know the pink line in the second display from the left, the one you plane is supposed to follow. Also, you can see how far away you are from the course (XTK, second page of PROG button on FMC).Well, sometimes it follows the line perfect, and other times it will not stay on it very well, like the flight I am on right now, it is like 2miles off the line. These are the WP1 direct routes, and there is only 200-300 miles between them!

This is a known issue. The ND will draw a straight line between the two waypoints, but the FD will steer a great circle route from point to point. On legs with a large distance between waypoints, the difference between these tracks can be large. I'm not sure if this is slated to be fixed in the 800/900 release or not.Aaron