In a programming interview, you might be asked how you'd weigh a 747 aircraft without using a scale of any sort. What follows is the correct answer:
Empty the plane's gas tank. Fill up the plane's gas tank. Note how many gallons of gas you used (calculate the mass of of the gas, as well, as you might not have time later). Get in the plane, take off, climb to altitude. Put the plane into a nosedive (turning off the engines will make the estimate more accurate). Measure the terminal velocity of the plane. Now dump all of the gas. Measure the new terminal velocity.
The ratio of the square of the two velocities is equal to the ratio of the two masses (plane plus gas versus plane). From there it is simple algebra. Depending on your algebra skills (and the initial height of the aircraft) you should be able to complete the calculation before hitting the ground.