The Smithsonian 3D Explorer can do far more than just displaying a single 3D model. One of it's most important features is the ability to compare different objects side-by-side. This feature is called split view, and you can find it in the setup toolbox.
1 Single view mode: displays one model in 3D or 2.5D mode.
2 Vertical split mode: You get two viewers in one, to view and compare either two different views of the same object (try a 3D view on the left and a 2.5D view on the right). Or you can load a different object in the second pane and compare the two objects side-by-side.
3 Horizontal split mode: Same as above, with two views stacked vertically.
4 If you are in split mode you can use the browse button to load a different model for each view. First click the view to activate it, then hit browse to open the mini-browser with all available objects.
5 Some, but not all objects consist of multiple parts. Try the Wright Flyer as an example of a multi-part model. In this section you can toggle the visibility of individual parts.
6 Most objects come with a wealth of background information. This section allows you to filter which annotations and pins you'd like to see and explore.