Watch a price die

The value of the workshop as one resource's stock changes, traced out in full. The marker is where the workshop currently is.

Try this. Take the planks past 45. The curve goes flat and the plank price drops to nothing — the saw has become the thing standing in the way.

The two rates are measured by re-solving a hundredth either side rather than by reading a formula, which is why standing exactly on a bend reports two different numbers instead of quietly picking one.