"1. What is the fuel flow on the A340 and 747- 400, and how is it measured."
Any particular phase of flight??? T/O? Climb? Cruise? Descent? Fuel burn varies dramatically from phase to phase. Since fuel burn is sort of programmable through the Flight Management Computers, this also dramatically affects fuel flow. You could set up the aircraft to give you max economy....or minimum time to destination.
On glass-cockpit aircraft, units of measurement are optional (the display computers are simply reprogrammed as required). Fuel flow can be lbs/hour or Kg/hr.
If by "how is it measured" you mean what kind of mechanical/electrical device is used to measure fuel flow, then...
On some aircraft, a sort of mini propellor is stuck in the fuel pipe going to the combustion chamber. The greater the fuel flow, the faster the propellor turns. The rpm is converted to a theoretical fuel flow value for display in the cockpit.
Rgds.
Q.