This simple precision micro-gram measuring system is yet another proof that humans can be so creative, and creativity alone can explain why we are the dominant species on this planet.
A closed feedback loop controls the position of the needle of a hacked mAmp meter. A thin piece of foil is used to break the beam of an LED-Photo transistor pair. And an amplifier is used to provide readable feedback from the loop. And that's it! You have a precision micro-gram measuring system, something that i bet one has to pay an arm and a leg to buy.