XP, G'day!
There is also a theoretic way of calculating thrust at alt/speed if you have SFC and FF data (not that I remember how )
You mean this? 200 lines of QBasic to derive CDc and one page of Excel to derive the rest?
By recommending Tom Benson's applet which neither asks for nor deserves approval for real-life use you run the risk of crossing the line between cyberspace and meatspace.
I mean for the best but I feel I still have to interject. The samples I illustrate are correct and open for verification. Tom Benson's applet is neither.
Best Rgds
the "E"