http://www.skybrary.aero/bookshelf/books/552.pdf - thats the 707 accident report. Guys measured density with defective meter, and estimated baggage weight wrong. Also looks like they aborted takeoff above v1. As usual in accidents - many factors summarized.

I never thought that refueling aircraft is so "lots of calculations" thing  :o
I thought - you fill the gas and go  ;D

And the tables above is in kilograms, while we using pounds mostly. And max tank volume measured in gallons. So you'll need density in calculations....have something to calculate before flight (in addition to many other stuff)

As for FSX - i'll try to use all that calcs. FSX dont require it, but it looks interesting practice 8-) I guess fuel usage not depends on fuel density, so the mass of the fuel is main thing for engine.

And those figures above - they need to be thinked about, but i guess one flight can make it clear, and i guess that we'll have much more satisfaction if we'll figure it out ourselves ;) Right guys?