Accurate weighing scales using hinge joints and rigid bodies

Hello! We're working on a physics-based VR shop game and we need accurate weighing scales like the type you'd find in your great grandmother's house. We have some working sort of... but they don't balance out nicely at all and often move very quickly with the slightest weight change (mass 1kg placed on plate).

I'm new to hinge joints, what would be a good configuration of them? In the pictures, there is a joint attached to the top bar with it's corresponding components. Many thanks!