For any learning sim, one goal is to create a strong microcosm. In this short sim, designed to introduce demand curves to students, the player can raise or lower the cost of a drink, or have the sun come out or go behind a cloud, to change demand and generate a standard demand curve.
The demand is visualized dynamically by the length of the people in line, with shadow highlights. The traditional demand curve serves as a mini-map to reflect the situation, with a yellow highlight showing the exact current position.
In this situation, different kinds of characters are waiting in line, and others are not. As the price goes up, only the most thirsty and those with the most money remain.
The interface is very simple, and allows for the player to navigate towards to objective, stated clearly, to find a situation where demand = 7.
There are some subtle elements as well. In the conditions above, a female is dragging a male to get a drink. As the price goes up, the male decides it is not worth it, leaving a thirsty buy unhappy female still in line.
Note: Temperature shifts the demand curve. For a mnemonic device, higher temperature moves the curve to the right, hopefully making it easy to remember for other situations.