Or maybe just a powder balance. When I was a kid in the 1960s, Dad did a lot of reloading his own ammunition. We kids had fun doing things like weighing our names (weigh a small piece of paper to get the tare, weigh again to get the loaded weight, subtract) and other miniscule things. As I recall, it was accurate to less than a grain (0.065 gram).

One of the things we did was weigh different shapes of paper to calculate area. Start with a sample of a unit area. Cut out a funky shape and weigh it, then do the math.