The attached gif is of a chart I've got in Excel, mapping Optimum/Maximum FLs verses Gross Weight (lbs). I loaded her to MTOGWand watched the VNAV page as I decreased the fuel loading.Much to my chagrin, I intended to decrease the lowest charted weight by restarting the test run with an empty payload and exactly enough fuel to match the lightest test data obtained in the first run. However, the VNAV page displayed an optimum FL that was 2000 ft higher at the same gross weight (the only difference is different zero fuel weight).Must be more to this calculation than simply gross weight.

It is very good. Thanks for your excellent work. I printed it out.Matyas Majzik

Dan,great job done.yes there is a slight difference between boeing dispatch and performance manual and FMC.we noticed that when we made the FOC danur 2003 profile for 744 GE but i still dont have the clue about this difference.the pmdg users gave this feedback. and i noticed too when i became one fo them too ...see youPhil