I have a FS450 in my aircraft linked to the GPS. When I get to the top of the climb and trim for the cruise I put cruise config and finish the lean (I lean in the climb to airways height), at this point I check the fuel flow against the laminated excel sheet I created from the POH. At 10,000ft indicated airspeed of 120kts I am doing doing 32lph. This is bang on with book figures. The FS450 is accurate to a fraction of a liter when I refuel.