Which boxes are empty?

This story was told by one speaker during the 2003 Oath Taking of new agricultural engineers. Unfortunately I forgot the name of that speaker.

A soap manufacturing company was having problem regarding empty soap boxes that were dispatched out of the facility. The empty boxes that passed through the manufacturing line occured frequently that it alarmed the company management. They then invited engineers and inventors to find solution to this problem.

An electrical engineer came and presented a technologically advanced scanning device. The device was designed to see through the boxes and thereby determine whether a box is empty or not. The members of the board were amazed by the technology and were even more amazed when the engineer presented the price of the device. Too expensive!!!

Next, a mechanical engineer came and presented a weighing scale which could be installed at some point in the conveyor lines. Much simpler! Empty boxes should weigh less, however, considering the modifications required for the conveyor lines in order to install the equipment, the cost is still too expensive overall.

Finally, an agricultural engineer came in... and to the committee's amazement, he brought in nothing at all. All he did was demonstrate to the committee how light empty soap boxes can be blown away using an electric fan.