This applet demonstrates the idea of [b]consumer surplus[/b]. It shows a simple, discrete demand curve, and allows you to adjust the market price level (the purple line) up and down. Consumer surplus is the total differences between what consumers are willing to pay for the burrito and the actual price that they pay (the market price). So, it's basically the area of whatever blue boxes appear. For a continuous demand curve, we can find the area via calculus (in particular, integration).