Is it really that hard? You make a lever/beam with notches at regular intervals. Move the hooks to set the ratio, and you can compare weights of arbitrary ratio

Is it really that hard? You make a lever/beam with notches at regular intervals. Move the hooks to set the ratio, and you can compare weights of arbitrary ratios. Sure there's some loss of precision at each step, but assuming you minimize the stacking of errors and return to the master reference whenever possible, I'd imagine it to be precise enough for pre-scientific uses. Note that many old measurement systems use factors other than 10, which happen to be easy to multiply/divide with ratios of 2 and 3, which happens to be very easy to make levers/beams for.