If you thought the viewing modes in the Library module were useful, wait until you get up to speed with the ones in the Develop module. Not only can you view your images with the standard Loupe single image mode, but the Compare mode is simply awesome.
The most commonly used view is the Loupe view, which displays a single image that is easily magnified via the Navigator pane, a click of the mouse, or the Zoom slider in the toolbar. Figure 4-17 When you enter the Develop module, you'll be taken to the previously used view mode. Select the Loupe view icon (circled) or use the D key to bring you to the Loupe view. (In the Library module, pressing E took you to the Loupe view.) Control informational overlays via the Develop View Options dialog box. (Develop→View Options)
The Compare view icon is found in the toolbar, sandwiched between the Loupe view icon and the Crop Overlay icon (circled). Figure 4-18 If you click on the triangle you will see a pop-up menu that shows you Compare choices. (If the toolbar isn't visible, press the T key to reveal it.)
You can select the compare view of choice from the pop-up menu or by clicking on the compare icon cycles through the various options ...