The statement that military fuel mass is not accurate is total bull. The fuel systems in modern fighters or bombers feed centre of gravity into the fly by wire system, so an accurate knowledge of the weight of fuel in each tank is needed.
For this reason, the fuel system on EFA (for example) is categorised as a level 1 system (failure likely to lead to total loss), while those on civil aircraft are generally level 2 (failure likely to cause divert and stress in cockpit).
On the civil side, the accuracy specified for the B777 was +/- 2% through the range of loads in the tank, with (from memory) +/- 0.5% close to empty.