This interface compares Levels and Curves. Level corrections can be easily mimicked in the Curves dialog. Rolling over each black dot in the histogram will create a different Levels correction. The equivalent Curves correction will be dispalyed in the Curves dialog at right.

The picture above shows what's going on. It maps the different movements of the sliders with color coded arrows. The arrows are also sumperimposed into the Curves dialog to show the corresponding movement.