That supply curve? Your class made it.

Each student is assigned a buyer or seller role and may trade one unit. Their device shows their private value or cost. Buyers submit a maximum bid and sellers a minimum ask. Once both sides close, accepted bids are ordered highest first and asks lowest first. Those submitted offers become the plotted steps; they are not a claim to reveal everybody’s underlying values or costs.

The mechanism matches the highest bids with the lowest asks while the bid covers the ask, then sets one uniform price using the displayed clearing rule. Equal offers use last accepted submission time, then a fixed identifier order if times tie. Submitting an accepted offer is not a promise of a trade. Each person sees their own ordered step, outcome and surplus, including a loss when the price is unfavorable relative to their card.

The first book stays sealed while sellers read their corresponding second-market cost cards. Everyone then chooses a fresh offer. Buyers’ private values stay the same, but buyers can change their bids too. The second curves contain only the new accepted offers: missing responses are not copied from the first book or replaced with zeros.

Compare the two books on the same chart scale and use the actual outcomes as evidence. Costs, offers and participation may all differ. The lesson does not guarantee a direction of price or quantity change, estimate demand elasticity, or compute how much one person caused the market price to move. A no-trade outcome has no transaction price, rather than a price of zero.

Try the screen-and-phone preview with fictional classmates, who submit their offers through the same runtime as the lesson. You run the projector’s steps and play one student’s phone, entering that student’s own offer, and you can run it again once it ends. The classmates are illustrative, not observations of real students. Shared accepted orders have no names, but a recognizable offer is not guaranteed anonymous.