It shows the difference between consumers' maximum willingness to pay, and the amount they actually paid. It shows the difference between the minimum producers were willing to accept, and the amount they actually got. There are four kinds of shifts that can happen. People find out kiwis cause bad breath. F. Shifts versus movements along a curve.
Students often have trouble translating changes correctly.
How to tell the difference. Think about whether the posited change makes people WANT a good more or less. If so, it's a D change. I. Canonical table, plus some examples. The supply of DVD players increases.