It's more comprehensive than just weight or percentage, you can actually point to a tank with the mouse and roll the mouse wheel to increase the quantity in each tank. For example the b17 you can fill any tank as much or as little as you want as you get a visual indication of how much fuel is in each tank. It is very useful for aircraft with multiple tanks spread throughout the fuselage and/or wings. I was hoping there was a similar way of filling each tank in dcs or at least knowing if there was fuel in the rear. I know about the spits top and bottom tank and how they feed.
I could do without the fancy visual display, even just having a percentage quantity for each tank would be useful. Assuming of course that this spit has rear tanks which I'm not sure has been confirmed either way!
Chris