Once I get to the halfway mark with fuel then I start to use the following info buttons in the GUI;
1. "Max range at current speed"; and
2. "Range to destination" (to last plotted point).
I plot my remaining patrol time around those two indicators (i.e. plot a search pattern/route etc then make sure my last waypoint is at my home base). Then I'll compare the reported distance given by 1. against the reported distance given by 2. I'll either adjust my patrol route or speed to ensure 1. is greater than 2.
You're probably already aware of that so apologies if I'm stating the obvious.
