system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do scales that are capable of measuring incredibly tiny amounts of things actually work?
gpt
I believe that most scales contain a piece of metal with a precise thickness/strength (called a load cell). Placing an item on the scale bends that piece of metal *very* slightly. By measuring how much the metal bends, you can figure out how much the item weighs. *How* that measurement is made is a little beyond ELI5, but it's done electrically by passing voltage through a set of resistors attached to the metal whose value changes when they're bent. By precisely measuring the voltage changes across those resistors, you can measure the distortion of the metal and thus calculate the weight.  
To measure smaller things, you need a smaller load cell (that will bend more from less weight) and very precise calibrated electronics capable of accurately detecting equally tiny changes.