just like most precision equipment, microgram scales are usually extremely expensive. The close tolerance machining of sapphire pivots as well as computer manage add to the cost. Not all of those elements are necessary though. This article from scientific American demonstrates exactly how to develop a simple microgram balance utilizing a salvaged galvanometer. when calibrated, the output voltage will have a direct linear connection to the weight. There is a more recent version of this job that utilizes a microcontroller to overcome static friction as well as auto center.

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